The type or namespace name could not be found [duplicate]

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..

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.