dll and system recovery

I recently upgraded to Windows XP pro fro Windows XP home.
I can not open the system restore file. I get the
following message:
The procedure entry point remote assistance Prepare System
Restore could not be located in the dynamic link library
WINSTA.dll.

Help, what does this mean. And more to the point, what
file have I lost that I can't open System Restore?

Thanks for any help.

Janet