RPC Server Not Available?

To enable a user to access an HP Design Jet 750 plotter, I must give him administrator rights to use the printer. Why should this occur? If I make him into a normal user, he can no longer get to the plotter and the system reports that the “RPC Server is not available”. The printer is properly shared out and I have reloaded the 750 driver numerous times and this problem returns within a few days. Printing is completely normal if this user has administrator rights. From a security standpoint, Iwill not be able to tolerate this for very long. It is WIN NT Workstation with SP5 peer-to-peer. Thanks for the help. This question is important to me and I have no clue how many value points to assign.

rick.westerfield@barksdale.af.mil