Hi Awinish
UBCD4Win = a BartPE type cd based os - there's a link to it in your post with the link above.
As time ran out we began a repair install last night to attempt to preserve the programs installed on the server (as they are missing original software media). The databases they run were vital. The repair has worked OK and we are back in with no loss of AD or Exchange so far. Not ideal but best of a bad job considering their backups and the state of the server in the first place.
The customer who owns this DC operates in a small business environment and cannot afford the luxury of 2 dcs hence a single SBS2003. Their previous IT supplier has let hem down and we were asked to salvage this situation. They have requested a new server from us today which will be built with SBS2008 and then we will migrate their data next week.
I have never come across this netlogon error ever before in 10 years of working in this field and am disappointed as an MCSE that I couldnt find a fix after intense googling and asking for help at EE and on the Microsoft Technet forums. You would think someone would have found a way round the issue.
Thank you very much for your help anyway. C