The error above happend after a new XP Pro was setup in an existing LAN acting as a file server - (network is peer to peer)
The Node Username and passwords have been added into the XP File server and the permissions set on a shared partion which is on a 2nd Hard drive (not the System Disk). All machines are fully service packed, the file server is a fresh install and all other nodes are free from s**t ware as far as we know.
This has happened twice now. Restarting the XP server down resolves the problem.
Not sure if it's related but when I initially set the machine up, I had a static IP, mask, gateway & DNS setup and the machine could not join be accessed from the LAN Nodes - but could be seen!
I have been trawling the web for some more information on this and it seems many have had the same problem on various platforms and LAN setups. Still cant find anything definative.