Windows Phone 8.1 - WACK error

Hi there,

when I'm building the app I get this error through the WACK:
API=System.Reflection.MemberTypes. Modul=MSCORLIB, PUBLICKEYTOKEN=B77A5C561934E089. Datei=Boo.Lang.dll

I saw another thread with this discussion and it is mentioned that this was fixed since Unity 4.3.3...

Any ideas?

Specs:
Unity 5 b13
Windows 8.1 pro
Visual studio 13

Log:
"Template.exe" (CoreCLR: .): "C:\Data\SharedData\PhoneTools\AppxLayouts\36774Name.NameVS.Master_x86.Dominik\UnityEngineProxy.DLL" loaded....

Windows Phone 8.1 - WACK error