There is a few things to check make sure your gallery folder is still writable.
Make sure GD is installed in PHP that alllows you to resize images.
Check your gallery path under gallery settings should end in /gallery/
It has worked so far. Suddenly no more... ...or not always (?)
Now it works again.
But some Thumbs are missing. Can i still generate them?
it´s done - simple regerated... thanks!
Nice glad you have it working again.