I have VB library that references C# library. C# library has a few classes with namespace FSWeb. And a few VB modules called this classes without any problem.
When I've added to the VB Project a new class with the same namespace specified, the c# classes became invisible in all VB classes for both compiler and intellisence with the errors like:
Error 231 'Search' is not a member of 'FSWeb'.
Error 230 Type 'FSWeb.LoginHelper' is not defined.
When I type “FSWeb.” intellisence shows only the class from the current VB assembly.
The workaround is obviously use different namespaces for different assemblies.
I reported this to MS as a bug.