Accessing UNC Path Uses Port 80 Instead of 445 (SMB/File Sharing)

Question

I can access \\SERVER2 fine, and watching the packets, I see it uses NetBIOS name resolution, and then uses SMB to communicate shares/printers etc.

When I try \\SERVER1, I see it uses NetBIOS name resolution, and then it sends a request on port 80, to which SERVER1 replies with RST, ACK. Windows then throws an error saying "The specified network name is no longer available". Using 'net use' I get Error 64.

Interestingly, if I use the IP address, it uses SMB correctly.

I turned off the WebClient service and tried, but received the same error.

I am yet to try a computer restart.

All machines are Windows XP.

UPDATE: I moved the 'Web Client Network' (WebDAV) up the list of providers, and noticed the same traffic on port 80 for \\SERVER2. After the failed RST, ACK, it then completed the connection on port 445 correctly.

I can only surmise that for \\SERVER1 it is simply skipping using 'Microsoft Windows Network' (SMB/LanmanWorkstation) provider for some reason.