Thanks for the reply nerbert.
I've tried using it anyway, but it gives me an error message saying I haven't selected anything.
I'm now also having an issue with if I move one manually and unticked the box so a "MOVED" thread notification isn't left behind, it still leaves one anyway... and if I delete that "MOVED" one, it actually deletes the real thread too. Which isn't good.. because I didn't realise it straight away and ended up deleting two important ones.
I'll have to look at what mods I installed and see if I can work out what one is causing these issues.... as I only have a week to find it and fix the problem (I reopen my website in 1 week).