Thanks for your answers
@Zx7R: I now tried to change the reference to Dll’s. Now I have some less problems. But still I have in one project this problem.
TFS is not installed. I use Tortoise SVN for source control. It doesn’t lock the file. I allready checked this with process monitor.
The event log doesn’t say anything.
And yes, I am administrator. So it isn’t a permission issue.
I now tried to make for each project a single solution and build one after the other. Result: I was able to build at least the half of the projects.