A colleague of mine imported some resources from one course to another using the Import link in the adminsitration block.

This was successful but, in addition, some links were created on the course page with icons but no text. When we tried to edit or delete these files, we got the error message

The required instance of this module didn't exist. Module deleted.

It looks like there are database entries for the items in the course sections without corresponding records for the resources themselves.

Others have reported this bug - discussed at http://moodle.org/mod/forum/discuss.php?d=100153#p442384 includes an example screenshot