Thumbnails sometimes not generating

Hello:
Everything worked fine and then, all of the sudden, no thumbnails were generated anymore. Sometimes a few, sometimes none.
Thew only thing I had changed was the way the permalinks are rendered. I changed it to custom, only the name of the post. This seemed to be the problem, changed it back even to one of the predefined, day and name of post and everything works fine again.

This post just for information and help to others which may experience the same problem.

Regards

Andre

http://www.HulstaertPhoto.us