Pending Archive Shortcut to Zero not cancelling items

I've got a mailbox with over 6000 items pending that I need to cancel. 

If I bulk select within outlook I get the following error. It will let me do about 100 items at a time which is a bit time consuming. 

I thought I'd try setting the pending shortcut timeout to zero but I cant seem to get it to work. 

I've set to zero, synched the mailbox , then run report mode on the mailbox in question but after 30 mins all the pending items are still in there. Should I see something in the Event Log on reports folder because im not seeing either ?

Thanks