It might not help you... but I have found with time, that sometimes, some actions were allowed in the past with the Admin client, which are not allowed anymore...
creating some inconsistencies at the database level.
And when you try to delete folders/application groups/application/users/... then the admin client will simply crash without giving any clue...
One time I had the problem that some application group field mapping were duplicated in the database, which should NEVER happen... but it did... and creating lots of problems.
Another problem was that for some objects, you has some left over of rights, with no user associated with it... creating a crash everytime you wanted to modify or delete a folder/application group...
Another time, in a field definition of a folder, one bit of the mask field of a folder field was wrong... should be there. Was is a database problem, a disk problem... don't know... but it was simply wrong. By clearing this bit, everything was fine afterwards.
I have no idea what is causing your problem, but maybe there are some inconcistency in your database.
So as Justin is saying, try the latest greatest version of CMOD Admin client (V9.5.0.7 at the time of writting if I am not wrong), and if you still have a problem, my advice would be to open a PMR, because most probably you might have a more deeper problem.
Regards,
Alessandro