Ok this is caused by the upgrade of VBulletin 4.1.0 PL2
The problem is that this version was issued because of a security risk so I really don't want to revert back... in fact I shouldn't have to.
Anyway if it helps I have tracked down where the problem is... but not what.
I think the problem is with the "class files" in Vbulletin> includes
I can't be any more specific than that.