The type or namespace name could not be found

Question

I have a C# solution with several projects in Visual Studio 2010. One is a test project (I'll call it "PrjTest"), the other is a Windows Forms Application project (I'll call it "PrjForm"). There is also a third project referenced by PrjForm, which it is able to reference and use successfully.

PrjForm references PrjTest, and PrjForm has a class with a using statement:

using PrjTest;

Reference has been correctly added
using statement is correctly in place
Spelling is correct
PrjTest builds successfully
PrjForm almost builds, but breaks on the using PrjTest; line with the error:

The type or namespace name 'PrjTest' could not be found (are you missing a using directive or an assembly reference?)

I've tried the following to resolve this:

Removed Resharper (since Resharper had no trouble recognizing the referenced project, I thought it might be worth a shot)
Removed and re-added the reference and using statement
Recreated PrjForm from scratch
PrjForm currently resides inside the PrjTest folder, I tried moving it to an outside folder
Loaded the solution on a different computer with a fresh copy of VS 2010

I have done my homework and spent far too long looking for an answer online, none of the solutions has helped yet.

What else could I try?

Wouldn't you know it: http://stackoverflow.com/questions/4286599/referenced-project-gets-lost-at-compile-time Turns out this was a client profiling issue, I didn't even think to check for that.. — Anders, Jan 21 '11 at 23:45
@Shekhar_Pro: I'm sure, it was one of the first things I checked.. — Anders, Jan 21 '11 at 23:46
Yep... this is generally a `.NET Framework` incompatibility\mismatch thingy. The problem is that Visual Studio (even 2013) won't tell you that in the `Error List` output window. :( — Leniel Maccaferri, Jul 01 '14 at 15:15
I've closed this as a duplicate because after careful reading your issue was the exact same one as the duplicate which pre-dates this question by 6 months. (Your issue was a client profile assembly referencing a full framework assembly). — slugster, Jan 23 '15 at 01:05
@slugster: I wish I had seen your answer a long time ago, it would have saved me a lot of trouble. I guess the trick is knowing the keywords to search for... — Anders, Jan 30 '15 at 23:05
I had the same issue in Visual Studio 2019, all I needed to do was to restart VS2019 and it worked. — Serhat, Nov 20 '19 at 13:45
Check in the .csproj file of that cs class that you might have changed recently. You need to push that. — Rehmanali Momin, Dec 16 '19 at 15:17
Spent a day trying to find a solution for this. Did everything I could think of and everything that the internet suggested to me. Nothing worked. Fixed it by restarting my PC. — ngstschr, Aug 25 '22 at 13:48

score 745 · Accepted Answer · edited May 23 '17 at 11:33

745

See this question.

Turns out this was a client profiling issue.

PrjForm was set to ".Net Framework 4 Client Profile" I changed it to ".Net Framework 4", and now I have a successful build.

Thanks everyone! I guess it figures that after all that time spent searching online, I find the solution minutes after posting, I guess the trick is knowing the right question to ask..

edited May 23 '17 at 11:33

Community

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answered Jan 21 '11 at 23:52

Anders

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Same error, but in my case I was trying to use a 4.0 dll in a 3.5 project. – Mikey G Apr 09 '13 at 20:32
6

Same error, but here it was 4.5 dll in 4.0 project. – CW30Meters Nov 26 '13 at 14:15
4

This happened to me last week but from loading a 4.5.2 library in a 4.5 project. Just a note: A 4.5.2 project can load a 4.5 or 4.5.1 library just fine. – ahwm Jan 12 '15 at 16:13
from where can I change the framework as you have described? – Kinjan Bhavsar Apr 14 '16 at 06:44
@KinjanBhavsar: it's in the project properties – Anders Apr 14 '16 at 16:52
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Thank you! scratching my head for an hour! I accidentally added a 4.6.2 proj and not 4.5.2. – Tez Wingfield Sep 11 '16 at 13:22
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In my case it was happening because the CS file was not properly added to the csproj. Re adding the class file to the project fixed the issue. – Sal Sep 04 '18 at 15:09
https://learn.microsoft.com/en-us/dotnet/framework/deployment/client-profile According to this "Starting with the .NET Framework 4.5, the Client Profile has been discontinued and only the full redistributable package is available. " – Pranay Aryal Sep 12 '18 at 19:04
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could someone add a screen shot or a good description of how to change PrjForm in VisualStudio2017. I have looked at every tab in the project properties and I don't see anything remotely named that. – Be Kind To New Users Jan 04 '20 at 19:09
On my side I was needed to downgrade the project .NET version and it worked. Thanks for the inspiration. – Idoshin Aug 31 '23 at 05:12

score 73 · Answer 2 · answered Nov 28 '12 at 04:01

73

In my case I had:

Referenced DLL : .NET 4.5

Project : .NET 4.0

Because of the above mismatch, the 4.0 project couldn't see inside the namespace of the 4.5 .DLL. I recompiled the .DLL to target .NET 4.0 and I was fine.

answered Nov 28 '12 at 04:01

DeepSpace101

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One of my projects was updated from 4.5 to 4.5.2 and triggered this issue.... – Vee Aug 02 '21 at 17:24

score 42 · Answer 3 · edited May 23 '17 at 12:18

PrjForm was set to ".Net Framework 4 Client Profile" I changed it to ".Net Framework 4", and now I have a successful build.

This worked for me too. Thanks a lot. I was trying an RDF example for dotNet where in I downloaded kit from dotnetrdf.

NET4 Client Profile: Always target NET4 Client Profile for all your client desktop applications (including Windows Forms and WPF apps).

NET4 Full framework: Target NET4 Full only if the features or assemblies that your app need are not included in the Client Profile. This includes: If you are building Server apps, Such as:

ASP.Net apps
Server-side ASMX based web services

If you use legacy client scenarios, Such as: o Use System.Data.OracleClient.dll which is deprecated in NET4 and not included in the Client Profile.

Use legacy Windows Workflow Foundation 3.0 or 3.5 (WF3.0 , WF3.5)

If you targeting developer scenarios and need tool such as MSBuild or need access to design assemblies such as System.Design.dll

In my case, I had 3 projects in 1 solution. I had to set them all to .Net Framework 4.5 and then I could compile! Its annoying that the error message was misleading. — rf_wilson, Jun 10 '14 at 12:25
In my case, this all did not help. However, creating a new project, installing the same NuGet packages and copying the code did the trick. — Rich_Rich, Dec 07 '18 at 15:29

score 41 · Answer 4 · answered Oct 15 '14 at 02:56

Another thing that can cause this error is having NuGet packages that have been built with a newer version of .NET.

The original error:

frmTestPlanSelector.cs(11,7): error CS0246: The type or namespace name 'DatabaseManager' 
could not be found (are you missing a using directive or an assembly reference?)

Further up in the log I found this:

C:\Windows\Microsoft.NET\Framework\v4.0.30319\Microsoft.Common.targets(1605,5): warning MSB3275: The primary reference "[redacted]\DatabaseManager\bin\Release\DatabaseManager.dll" could not be resolved because it has an indirect dependency on the assembly "System.Data.SQLite, Version=1.0.94.0, Culture=neutral, PublicKeyToken=db937bc2d44ff139" which was built against the ".NETFramework,Version=v4.5" framework. This is a higher version than the currently targeted framework ".NETFramework,Version=v4.0".

The solution was to re-install the NuGet packages:

http://docs.nuget.org/docs/workflows/reinstalling-packages

this did it for me, my app was targeting 4.5.2 but unit tests were on 4.5 thanks. — actual_kangaroo, Aug 19 '15 at 06:12
This one! I had shut off warnings because, you know, WARN... Turned that back on and it showed the error straight away. — O'Mutt, Jun 27 '18 at 19:10

score 30 · Answer 5 · answered Dec 09 '12 at 13:41

30

I solved mine because the other project was coded with .NET 4.5 and the other one was coded 4.0

answered Dec 09 '12 at 13:41

kurdapya

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I had the same issue between .NET 4.0 and .NET 4.0 Client Profile. Good call. – Andrew Grothe Sep 10 '13 at 13:50

score 10 · Answer 6 · answered Jan 21 '11 at 23:40

10

The using statement refers to a namespace, not a project.

Make sure that you have the appropriately named namespace in your referenced project:

namespace PrjTest
{
     public class Foo
     {
          // etc...
     }
}

Read more about namespaces on MSDN:

Using Namespaces

answered Jan 21 '11 at 23:40

Mark Byers

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Thanks Mark, I do have the namespace appropriately named. – Anders Jan 21 '11 at 23:53

score 6 · Answer 7 · answered Jun 03 '13 at 07:05

I encountered this issue it turned out to be.

Project B references Project A.

Project A compiled as A.dll (assembly name = A).

Project B compiled as A.dll (assembly name A).

Visual Studio 2010 wasn't catching this. Resharper was okay, but wouldn't compile. WinForms designer gave misleading error message saying likely resulting from incompatbile platform targets.

The solution, after a painful day, was to make sure assemblies don't have same name.

score 5 · Answer 8 · answered Apr 24 '14 at 06:14

5

The compiled dll should have public Class.

answered Apr 24 '14 at 06:14

Peter

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score 5 · Answer 9 · answered Jan 31 '12 at 23:48

5

It is also possible, that the referenced projects targets .NET 4.0, while the Console App Project targets .NET 4.0 Client Library.

While it might not have been related to this particular case, I think someone else can find this information useful.

answered Jan 31 '12 at 23:48

Sebastian Zaklada

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score 3 · Answer 10 · answered Jul 30 '12 at 12:40

3

I had the same issue. The target frameworks were fine for me. Still it was not working. I installed VS2010 sp1, and did a "Rebuild" on the PrjTest. Then it started working for me.

answered Jul 30 '12 at 12:40

saju

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score 3 · Answer 11 · answered Oct 23 '13 at 14:25

Other problem that might be causing such behavior are build configurations.

I had two projects with configurations set to be built to specific folders. Like Debug and Any CPU and in second it was Debug and x86.

What I did I went to Solution->Context menu->Properties->Configuration properties->Configuration and I set all my projects to use same configurations Debug and x86 and also checked Build tick mark.

Then projects started to build correctly and were able to see namespaces.

score 2 · Answer 12 · answered Oct 01 '12 at 03:17

2

Changing the framework to

.NET Framework 4 Client Profile

did the job for me.

answered Oct 01 '12 at 03:17

Radix

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You bring up a good point: as long as all your projects are using the same framework, it should fix the issue - whether it's the client profile or an earlier version of .Net. – Anders Oct 01 '12 at 14:33

score 2 · Answer 13 · answered Oct 21 '12 at 17:30

For COM/ActiveX references, VS 2012 will show this error right on using statement. Which is quite funny, since it's saying that may be you are missing a using statement.

To solve this: register the actual COM/ActiveX dll even if it's in the neighbor project, and add a reference through COM channel, not project channel. It will add Interop.ProjectName instead of ProjectName as a reference and this solves this strange bug.

score 1 · Answer 14 · answered May 04 '12 at 10:28

1

just changed Application's target framework to ".Net Framework 4".

And error got Disappeared.

good luck; :D

answered May 04 '12 at 10:28

Hamed MotallebiNejad

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How to change the applications target name please? – A user Dec 08 '16 at 15:34

score 1 · Answer 15 · answered Dec 03 '12 at 22:34

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check your Project Properties, your Reference Paths should be empty like this:

Project Properties

Regards

answered Dec 03 '12 at 22:34

Luis Rodriguez

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Adding references folder of the problematic reference dll via this screen solved my problem. I guess problem is different versions of references of first level references. – Gökhan Ercan Apr 21 '20 at 11:08

score 1 · Answer 16 · answered Jan 22 '11 at 00:48

1

If your project (PrjTest) does not expose any public types within the PrjTest namespace, it will cause that error.

Does the project (PrjTest) include any classes or types in the "PrjTest" namespace which are public?

answered Jan 22 '11 at 00:48

Reed Copsey

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Thanks for the insight, I'm learning a lot about this. PrjTest includes around 50 public classes; it's a decent-sized project – Anders Jan 23 '11 at 17:40

The type or namespace name could not be found

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