So, I fiddled around and think I got it solved.
The default name for the initial run configuration when creating a new Test Suite is "TestRun".
I renamed this to "Default" some time ago and forgot about that.
Maybe, I renamed it later to "xxx" (but it still kept its ID in the background I guess)
Somehow, it seems to fail on a latter stage, when the default name is not available anymore?
I created a new
test suite, moved all content into it and deleted the old test suite.
So there is only one configuration named "TestRun".
This way, I can run it by using command line:
I renamed the test configurations up and down, but I wasn't able to get the exe to fail anymore - but anyway - it works now.
: got it
If you change the name of the default "TestRun" run configuration, the error appears when double-clicking the executable or running from command line without parameters.
If you specfiy the /ts parameter on command line, it runs normally.
Sounds like a bug?