I've seen quite a few of those.
Much of the time it is OK the next time I try it. Bt it is a signal to me to close everything and start Alibre again. That usually prevents it happening again.
It MAY happen more after a fair bit of work with largish files..... maybe the old memory leak issue yet again? I mean there IS a leak, the question is what happens when you get to the point that the OS is swapping memory to disk and back?