[VS2013] Build fails when Deploying a wsp with included dlls

Hey guys,

I have following problem when i use the new VS2013 instead of VS2012:

When i click Deploy (to the local Sharepoint 2010) the Build fails with error
"The type or namespace name 'DataAccess' does not exist in the namespace '<project namespace>' (are you missing an assembly reference?)"

This occures when i include the "DataAccess"-dll in the Sharepoint package with GAC-Deployment. If i remove the dll from the package, everything works fine.

Does anybody know why i can't include the dll in the package? It works fine with VS2012.

Greetings,
Sebastian