MissingMethodException in multi-project solution

[Tim Anderson]

I have a multi-project solution imported from VS 2003. It includes an exe
and several dlls.

If I add a method to a class in a DLL project, and then call it from exe
project, this is picked up by intellisense and I can successfully compile.
However when I try to debug I get a MissingMethodException on the call to
the new method (it is a public method of a public class, so it is not a
visibility issue).

I've tried Clean, and rebuilding each project individually, and still get
the problem.

Any ideas what is causing this?

Tim