Hmmm, try what Aaron has suggested, that could be the solution...
Please keep posting back and letting us know..
We will fix this...

I've installed the new codec and I still get the error message. Is there anything else I need to do once I've installed the codec?

Ok...Try removing Santa and all traces of it off your computer and then download it again http://www.dvdsanta.com
We will see if that makes a difference now...

No such luck! I uninstalled, restarted and installed it again but still got the error message.

I'd be happy to use remote assistance, if anyone is willing and thinks they might be able to get more of an idea of what's wrong.

Ok what happens when you put an old file in - one that you have already burnt successfully, does the error still come up..