Please mention the steps to reproduce this issue in Creator4.1 Update1 for us to investigate
I have regulary open 4 to 8 instances of Creator 4.1 and never had any errors.
Running Windows Vista or Windows 10. Are you running a virtual OS as VMware?
@anks: I tried to reproduce it, but currently it seems to be stable. Still investigating. As soon as I have such a behaviour again, I'll report.
@Bob: No VM or anything else. The affected workspace contains about ten projects, build is always made for current project, not whole workspace. At the time when the error occured, I had a 2nd instance open with a single USB project to review a code snippet. But nothing obvious which would explain the behaviour.