C# Annoyance

I'm blogging this for my own damn good, since I never seem to remember the solution. I've frequently had an error recently when referencing projects in C# stating something along the lines of:

The type or namespace name 'namespace' does not exist in the namespace 'other_namespace' (are you missing an assembly reference?)

And you know what? It's infuriating.

Turns out, the solution is similarly infuriating: check the target platform. The class libraries are, of course, built in '.NET 4', however the application referencing them is set to '.NET 4 Client Platform'. Why? Who knows. But if you change it to plain old '.NET 4' it fixes it.

Job done.