Cannot modify or delete images

At least one user can upload and insert images, but then nobody except the administrator can edit or delete them. Even a user with a role that has all node images rights cannot do anything with them. Other nodes do not have this problem.

I have already rebuilt the permissions, suspecting some error there, but it did not solve the problem.

Anybody else experiencing this? I recently upgraded Drupal from 5.8 to 6.6 and did that very carefully with disabling modules before and re-enabling them after the upgrade and running update.php before and after this re-enabling. I don't know what more I could do.

Hans-Georg