Ambiguous references with the exact same namespace

Question

The RC class is not linked to a database, it is a simple class. The class is at only one place and is not partial. The Aérochem.Domain dll project compiles just

Answer 1

For ReSharper users that, like me, don't want to delete their solution's *.suo file:

Clear your caches via: ReSharper -> Options -> Environment -> General -> Clear Caches!

Thanks go to AUSTX_RJL for his comment to this answer. I wanted to give his valuable info more visibility.