Compiler Error C3381
'assembly' : assembly access specifiers are only available in code compiled with a /clr option
Native types can be visible outside the assembly, but you can only specify assembly access for native types in a /clr compilation.
For more information, see Type Visibility and /clr (Common Language Runtime Compilation).
Example
The following sample generates C3381.
// C3381.cpp
// compile with: /c
public class A {}; // C3381