Have you checked the threads on your ASA and tank reg to see whether they are all okay? None of the threads are stripped are they? Also you may be cross threading and not screwing the tank in straight? They're the main obvious things I can think of off the top of my head.
is it an on/off asa or standard? if it is a standard one then it might just be stiff as you screw it in it has to depress the pin on the regulator.
no a nxt shocker but i think i found the problem looks like there a actully thread from a tank stuck in it haha
fixed it after many hours with a fine set of screw driver and a hammer managed to get the shard of metal out cheers for the help guys
just make sure it has fully been removed as you don't want it flying around inside your marker effin it up
maybe fixable if you can get the tank out of the asa, then have a look at the threads on the asa and see how much damage has been done. If there are loads of metal fillings and the threads look worn down probably time for a new one!
Ide say get a new one as if there is damage to the threads it would indicate the threads are now weak (hence the problem in the first place), plus you can't really go wrong with getting new