I ran into an issue on a Windows XP system where the RUN command for all Scheduled Tasks was disabled and grayed out. I needed to manually run one of my scheduled tasks, and could not do it. I am not sure if this is due to domain/local policies or registry trickery, but regardless I found a way around it. Microsoft included a neat little utility called SCHTASKS.exe under the C:\Winnt\System32 folder that will allow a user to control Scheduled Tasks from the command line. I had a task called CESL that I wanted to run, so to run that task, I ran the following command:
C:\winnt\system32\schtasks.exe /run /tn CESL
That took care of my problem.