PnP Software Device Enumerator (Code 31)

Hello all:

I have recently been baffled by a problem I've encountered for the first time with a customer of mine. I built him a PC recently and all was well until the other day his audio stopped working. I checked for driver conflicts, driver errors/corruptions etcetera. I found that the was actually no issue with the drivers themselves but with the System Device "Plug and Play Software Device Enumerator". It is giving a Code 31 error and after spending the best part of 4 hours scouring the internet for solutions I did the following;

1) Uninstalled the device and reinstalled it with the Swenum.inf and swenum.sys method.

2) Uninstalled the sound drivers and reinstalled them.

3) Tried a different non-onboard card (Which I know works)

4) Ran System Restore to several points including that of 3 weeks prior to the problem starting.

5) Banged my head off a wall.

6) Swallowed pride and posted for help.

I have come across a lot of people having this error presenting itself in a variety of ways. The majority of the solutions around point to driver problems with the audio hardware but this is clearly not the problem here. From a few places it seems that a few people think that problem arose from a MS update a while back but why now? And why is this not fixed my MS yet?

Anyway, any help would be much appreciated. I'll probable end up doing a complete format and reinstall.

Thanks.