Associations are disappearing

We are running Netware 6 and Zenworks 4 for desktops. We have a building where for no known reason a user’s association for a printer (NDPS) just disappears. This is happening randomly to different users. We have to go in and reassociate that user with the printer and it works. This is a real pain as it happens everyday to different users. Any see this and have a solution?