Just posting this in case in helps someone else, and perhaps someone will be able to explain it to me.

We have a farm of Citrix servers all running Presentation Server 4 on Windows 2003 on HP DL385 servers. Novell Client version 4.91 SP4. We found that one of the DL385 servers was giving problems when writing to any of our Netware servers (a variety of versions and all of which are on VMWare). In particular if you tried to copy any file > 1Mb to any of the netware servers, it would take forever and would frequently not complete. Using MONITOR you could see the connection dropping and immediately reestablishing itself. All other network traffic from this DL385 was fine. You could read files from a netware server and you could read and write to any Windows server.

A PKTSCAN on the netware servers did not show any particular errors. We tried all the usual things (another NIC, setting speed and duplex) but nothing helped. However when we disabled TCP Offload Engine (TOE) on the NIC (an HP NC 373i) the problem disappeared.