Okay Chuck, thanks for the direction as always.
Hopefully the licence renewal will be approved within the next 24hrs. I believe I'm right in thinking that once vBulletin process the payment I'll still retain the same vBulletin licence number, in which case I shouldn't need to alter any of the above and hopefully the Classifieds will continue to work as normal.
If this problem is caused by an expired vBulletin support licence, it maybe worth highlighting to you that the issue doesn't occur within 'Photopost Pro'.
I'll give you an update when I know more.