OK, now I'm really confused.
I thought I'd narrow it down to which one was wrecked before wasting any of you guys time and so moved them all out as James suggested. I put them back in 1 at a time and reloaded VOX each time to see which one was the cause.
I put them back in one at a time restarting between each and they all went in just fine without any freezing!?!
I restarted VOX three times just to make sure I wasn't imagining it. I have since scanned for new music and video and I still can't replicate the problem.
Bizarre.
I'll let you know how we get on. If it does it again then I'll send you the XML files but for now it seems to be working just fine
-P