Join form doesn't work following mySQL update...

It may be a coincidence, but I've found that our join form no longer forwards to the next page when you click 'join'... the page simply sits there with no movement... following our upgrade to the latest version of mySQL (which has depreciated quite a number of functions). We use a splash screen and cannot work out what's causing this 'error'... there's nothing showing up in error.log - the button simply does nothing. Here's a link to our login/sign-up screen.

Any ideas?

This issue was resolved by uninstalling the nicknames filter.