I have a Solution with a lot of projects and I rewrote one project with other technologies for which i had to change the target framework from .NET 3.5 to .NET 4.0. All my other projects are in .NET 3.5
Now none of my references seem to work anymore. I have 2k "Are you missing a using directive or an assembly reference?"-Errors
I looked at my references in my other projects and there was a little yellow exclamation mark on the one I changed, that looked a bit like this:
I tried to add the Reference again, some Errors were gone, but that little exclamation mark was still there
Am I doing something wrong? How can I get rid of that exclamation mark? Is it bad to have different .Net versions in one Solution? And will it work if i get my References right?