Strange Error - CS0012: The type x is defined in an assembly that is not referenced

Question

The type \'x\' is defined in an assembly that is not referenced. You must add a reference to assembly \'abc123\'.

I have a .NET 2.0 web application that references m

Answer 1

There's also a bug that can manifest itself with similar symptoms, described here.

The workaround is to delete everything in the C:\WINDOWS\Microsoft.NET\Framework\v2.0.50727\Temporary ASP.NET Files\ directory, and it only seems to manifest itself in debug mode.