Insufficient Sysem Source

I’m running window 2000 with service pack 1. Since I started the schedule backup from window 2000. I set it to backup everynight into my D: drive. Every time when I come in the morning. I tried to open a program it give me an error message “Insufficient system source exit to complete the requested services”. When I tried to shutdown the computer it give me another error message “You do not premission to shut down this computer” I have to CTRL+ATL+DEL to shutdown the computer. If anybody whose known what cause this problem please help me.

Thank you very much in advance for you help

Thomas