Hi Nikolay,
OK, you've caught a good one!
![smile :)](http://pixinsight.com/forum/Smileys/default/smile.gif)
This seems an easy-to-fix little bug: the problem is there are more working threads than actual images to be processed. Can you confirm that the bug does
not happen if you
remove the last three target images instead of disabling them?
I'll try to publish a fixed version of the ImageCalibration module ASAP.
Thanks for stressing things
![Wink ;)](http://pixinsight.com/forum/Smileys/default/wink.gif)