The type or namespace name could not be found

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?

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..

Stack Overflow Q#4764978, score: 753