Turn off Oportunistic locking and increase the cache in the Netware Client Settings.
OH, iffn you are not using the Novell Client for Netware... Download it and install it. You can be MUCH more analy retentive about how the client works that way and can usually nail it down.
BTW, before all this... Make sure the Client is running the same frame-type as the server... if the server has 802.2 and 802.3 bound to the interface... well ick.
I use exclusively Ether_II now. Then there is just one frame type the "hub/switch" has to deal with.