Novell Client with Windows XP

We are on a network of 200 + users running Windows XP SP 1a and Novell Client 4.9 SP2. We have some Win2K machines too and they have no problems at all. The XP machines have log in issues. The XP machines are Dell GX 270's and once in a while when you press control alt delete, put in your username and password, hit ok and it takes you back to the control alt delete screen. It does this over and over again and you have to reboot and it works ok. The other problem we have is sometimes when you click ok to log in windows doesn't load the desktop. You just get a blank screen with your background and nothing else. But you can log in "workstation only" and bypass logging in to Novell and everything loads fine. So I know there is a compatibility issue with Novell Client and Windows XP since this doesn't happen on W2K. Most of the time these machines work fine but once a week these symptoms occur. They are all brand new machines and it happens to all of the GX 260 and 270's since they are running XP. Does anyone else have these issues? Please help! We are running XP Pro with IPX only installed for the Novell Client. We had this same problem with the previous version of novell 4.9x sp1 and upgraded recently to sp2 in hopes it would fix our login issues. 2 days ago we discovered the NMAS setting and turned it off but it was installed by default during the installation. Is turning it off now through the settings the same or do we need to reinstall the client with NMAS turned off?