I sorted this! By reading your instructions! Who would have thought.
The problem was caused by the Firewall mod_security settings of the new host (Krystal). They were able to identify the event that was being blocked rather than disabling mod_security all together.
Thanks! Yeah Till Wiedeck designed that site, he's really good!
I'm gonna make a little change for the next update so it will work too, when you upload .woff files like "12345.woff" :D