Does anyone know good articles for integrating .NET assemblies into SQL Server?

I'm trying to create an assembly at the moment and I'm getting this error:
Code:
Msg 6213, Level 16, State 1, Line 1
CREATE ASSEMBLY failed because method "set_mobjClient" on type "fgoTest.Test" in safe assembly "TestAssembly" has a synchronized attribute. Explicit synchronization is not allowed in safe assemblies.
I really have no idea what it means and can't find any help on it.