Alias Stopped Working

Hi. We're now unable to save changes to alias entries. This has all been working fine up until today but SEF Advance alias function is no longer working - it's not saving any changes or accepting new entries. When I try to save, I'm presented with a blank screen. Can you help?

I'm attempting this on this site: http://www.adventure-devon.co.uk

Yet, bizarrely it's working fine on my other website http://www.adventure-cornwall.co.uk