Is there a way to delete all inactive users at once?
out-of-the box: no!
This is a hack that should be easy tho accomplish though, but what do you define as inactivity?
You'll have to disable the "remember me" option on login, so the user won't be recognized on every visit and is forced to log on each time, just to keep your activity log up to date (if you define activity by "visits to your gallery"). It'l become trickier if you define activity by participation via rating/comments/uploads...
GauGau
I think he means inactive users as in users that have not activated their accounts....
If so, just go to phpmyadmin and execute this query in the coppermine database:
DELETE FROM cpg11d_users WHERE user_active='NO'
Oh thanks! :)