Sorry not to have any more meaningful help, but the ‘check failed’ messages are not documented. I have a suspicion that even the developers at Cycling ’74 would have to search through the source code to figure out what sort of circumstances generate any particular check failed message. And that still doesn’t explain "what happened."
If you can provide a patch that recreates the situation, including steps (ie, make a complete bug report), someone may be able to look at it and stop it from happening in future. Some of us other normal users can also try it out to see if the error occurs on our systems (there are some errors that depend upon your OS, or your system setup).
ehm, so I did a new "Granu-A" and saved it in a different folder this time, my mistake in not trying this earlier.
While the "Granu-A" in the previous folder still gives this problem, the new one in another folder, DOES NOT give the problem.