Update thumbs problem

[marpessa]

Hey, we've changed our gallery's setting, and made the thumbs bigger and also added intermediate pics. So, we need to update our old albums by using the admin utilities.

It was working fine in the beginning, but then I started to receive this error:

Warning: chmod(): Operation not permitted in /home/virtual/site9/fst/var/www/html/gallery/include/picmgmt.inc.php on line 224
albums/MAG/2000/06_entertainmentweekly/thumb_001.jpg updated succesfully!
albums/MAG/2000/06_entertainmentweekly/normal_001.jpgupdated succesfully!

It says the thumb is updated but it's not actually. It still works fine with some albums, but gives this error with some others.

Help? Please?