User Moving/Pruning System
 

I'm using the User Moving/Pruning System and when I press the delete button of the users I want to delete I check the delete radio button and press the go button and then get an error message: invalid action

What am I doing wrong???

Need a little more info than that. A screen shot or the entire error message copied and pasted here.

If you are on a shared server, you most likely are only allowed to delete up to 1000 users at a time or your will get an error. So, set the criteria to only prune 1000 users at a time or change the php setting (something only your host can do) for max_input_vars