I was updating the usergroup permissions due to some spam accounts being created and filling their signatures up with links which show on your user profile page. As they weren't posting I hadn't noticed this happening so you now need 5 posts to be able to have a signature. However I appeared to have messed some stuff up and not created the correct permission on everyone in the new usergroup. I think I've fixed everything now, though please let me know if you can't do anything or spot something you think might not be working correctly. Sorry if I caused any problems to anyone by not being able to post or use PMs.