The documentation is clear enough:
Both the current assembly and the friends assembly must be unsigned, or both must be signed with a strong name. If they are signed with a strong name, the argument of the InternalsVisibleToAttribute constructor must include the full public key, as well as the name of the assembly.
See this answer for an example of what a full public key means.
FrΓ©dΓ©ric hamidi
source share