So, after waiting for a few days for a response from support, and still waiting, I decided to fix this myself by uninstalling (properly, by also deleting X1 & X3 folders and registry keys) and reinstalling both X1 and X3. This fixed the problem but I'd sure like to know what caused it in the first place!
Anyhoo, just thought I'd post this in case anyone else has a similar problem.
Cheers
Mark