Server: NW6.5sp3 + Post NSS and Server update - Dell 2600 dual 1.8 Xeon,
2.5GB, OpsLock and client side caching off

Client: Windows XPsp2 all patches, Client 4.91, Dell GX620 3.4Ghz, 1GB

Connection: TCP/IP, Switch Cisco 3750

Files sizes: The greater the file size the greater the chance of random
disconnects. Problem has occured with files as small as 70MB

When I copy from the server to the client everything copies fine. If I copy
from the client to the server it will randomly drop the connection.
Sometimes immediately sometimes after several GB have been copied. The
error message I get is:"Cannot copy FILENAME: The specified network name is
no longer available." If I drop to 100Mb the system copies fine. The cache
buffers on the server slowly decrease but normally there are over 150K
available when the system disconnects. I have tried copying the same files
from a MAC via AFP and the files copy fine everytime.

I have had this problem with Client 4.90, 4.90sp2, 4.91
I have tried the following settings on the client:
Burst mode - on / off
File Caching - off
Large Internet Packet - on / off
Signature Level - 1 / 3

Any Ideas?