WinXP SP1 cannot find Novell server

I have one Netware 5.1 & one Netware 6 file server on seperate networks. Both have only WinXP machines connected to them with no problems for about a year. I recently deployed 1 new machine in each network, using WinXP SP1 OS. I installed Novell XP Client V 4.831 on both. Both machines see & log on to their respective servers the first time I boot up. Once I log off, neither will see the server again. Both see the other Windows machines on the networks with no problems. The only differences in old & new machines is the old have XP Pro WITHOUT SP1 (it is installed later as an update) & the new have XP Pro WITH SP1. I have tried the windows client and the Novell V4.83 client with the same results. Anyone have any ideas?