Compiler Error C2261
A value was not valid.
InternalsVisibleToAttribute is used to specify a friend assembly. For example, if a.dll wants to specify b.dll as a friend assembly, you would specify (in a.dll): InternalsVisibleTo("b"). The runtime then allows b.dll to access everything in a.dll (except private types).
For more on the correct syntax when specifying friend assemblies, see Friend Assemblies (C++).