Cannot copy filename:The specified network name is no longer available

[tcprstreq]

I have a Windows 2003 Server that is acting as a PPTP VPN server. Whenever a file is transferred from the server over VPN to a Windows XP Pro system I receive the error message "Cannot copy filename: The specified network name is no longer available". I did some searching online and it suggested turning off NetBios over TCP/IP. I turned it off on both server and workstation and I still receive the error message. Sometimes it may take only a few seconds for the message to appear, and other times it may take up to 20min. I connected to the server using a Linux workstation and I get an error message "invalid command or parameter". Used Wireshark to monitor packets and it seems as if the server is sending a connection reset at the time:

server is 192.168.20.2 and the workstation vpn address is 192.168.20.60

25049,"608.250000","192.168.20.2","192.168.20.60","TCP","microsoft-ds > 2002 [RST] Seq=16985735 Len=0"
25050,"608.250000","192.168.20.2","192.168.20.60","TCP","microsoft-ds > 2002 [RST] Seq=16970615 Len=0"
25051,"608.250000","192.168.20.2","192.168.20.60","TCP","microsoft-ds > 2002 [RST] Seq=16973135 Len=0"

Steps that I have already performed to try to resolve
1. Updated server network driver and forced 100MB Full Duplex on network card.
2. Replaced switch and cabling.
3. Verified time was correct.
4. Updated firmware on server location main router and client location main router

Any ideas?