Hello,
I confirm the problem: when VS projects (originally VC9) are converted to VC10, version of .NET framework in CSharp projects is kept as it was (3.5), while in C++ projects it gets elevated to 4.0 (default for VC10). This causes incompatibility between the projects.
The solution is to change option "Target framework" in properties of C# projects (tab "Application") to ".NET Framework 4" manually.
I have registered an issue 24707 in OCCT bug tracker for this problem.
Commenter-1