The problem may be that the system has over 3G RAM. The 32 bit OS could not handle this, which is why running a 64 bit system overcame the problem, with better management of larger RAM blocks.
This could have also been tested by reducing the RAM down to 2G, as was documented in http://www.nvnews.net/vbulletin/show...highlight=9400
There may also be issues in 180.51 that remain unresolved to do with this. The 9400 GT seems to have only been added in the last two releases.