RDP Clients Lose Local Drive Mappings

I am running Server 2003. For some reason when my terminal service clients connect, for the first 3 or 4 days they do have access to their local hard drives on the PC’s they are connecting from. However, for no apparent reason they lose access to their local drives when they connect. I reboot the server, they are fine for a few days, then it happens all over again.

Has anyone run into this problem before?