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I'm getting this error thrown repeatedly on my IIS 6.0 server:

It is not possible to run two different versions of ASP.NET in the same IIS process. Please use the IIS Administration Tool to reconfigure your server to run the application in a separate process.

However, I ran an IIS MetaBase Analyzer to view all AppPools and AspNetVersions they're running and do not see any AppPools running different versions of AspNet. Is this a bug in IIS or is there definitely an AppPool running multiple versions of AspNet?

Thanks

mint
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    This would mean you have multiple applications (either sites or virtual directories) using the same appPool, but one of these sites/applications has a different .NET version setting in the .NET tab. You would have to create another appPool to use different .NET versions, or check all applications .NET settings again. – Brock Hensley Sep 20 '13 at 15:53
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    @dirt Correct, I understand the nature of the error but I've looked at every website and AppPool and do not see this happening. I see no AppPool that has multiple versions of AspNet running under it; that's what's making me confused. – mint Sep 20 '13 at 17:33
  • Try editing the .xml files in Notepad and searching for the version number you aren't able to find in the GUI – Brock Hensley Sep 20 '13 at 17:35
  • Unless you need applications to share an app pool, create an app pool for each application, including the default one (at root). I would guess your diagnostics don't show anything running 2 versions because the 2nd one won't start up & you won't observe an appdomain with two run times loaded – MatthewMartin Sep 20 '13 at 18:04
  • Could you upgrade to IIS 7.0 or 7.5? Here's a useful link: http://stackoverflow.com/questions/7551034/set-asp-net-version-to-3-5-in-the-iis-6-default-web-site-properties-asp-net-tab – Thiago Custodio Sep 20 '13 at 19:10
  • How many sites and applications (as in `/someapp`) are on your server? Forget metabase analyser, it doesn't really do a very good job at helping you work out ASP.NET version pool conflicts when, in the case of IIS6, you're encouraged to host multiple sites/applications in the same pool. – Kev Sep 20 '13 at 22:13

2 Answers2

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Although it's an old question, for the benefit of future users who visit this yet unanswered question, here is the solution that worked for me.

In my case, the following worked.

Symptom :

The ASP.NET tab, for the "Default Website" node of the IIS Admin was showing a version of 1.1. The ASP.NET tab, for my virtual directory application, was showing a version of 2.0 (which is the right one for my application).

Solution :

I changed the first one from 1.1 to 2.0. The application worked.

Cause :

The cause, however, seems "mysteriously unrelated", as it often happens in Windows. It was working fine with the same old (different) settings until a week back. What happened during the week, was that the machine A running the web server for my web application, had to unjoin a domain B and join another domain C, because the primary domain controller on B failed and had to be replaced with C. Why on earth would that affect IIS Admin or the web application hosted on A, and why it should generate this particular error is beyond me. Such a cause for this error seems undocumented.

Whirl Mind
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It is not possible to run two different versions of ASP.NET in the same IIS process. This would mean you have multiple applications (either sites or virtual directories) using the same appPool, but one of these sites/applications has a different .NET version setting in the .NET tab. You would have to create another appPool to use different .NET versions. To create another appPool and associate it to your application do (Windows Server 2003): 1.Click Start, point to All Programs, point to Administrative Tools, and then click Internet Information Services (IIS) Manager. 2.In Internet Information Services (IIS) Manager, expand , right-click Application Pools, point to New, and then click Application Pool 3.Right-click on application that uses a different .NET version and click on Properties 4.On menu Virtual Directory choose in the item Application Pool the application pool that you created in point 2.

Regards!

user6672842
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