Run As option missing

I am running xp pro and recently have noticed that the
run-as command is missing when I right click on a program
icon. The run-as command used to be available when
logged on the machine as a power user. I have checked
the secondary logon service and it is set to start
automatically, and is running, but the command will only
show if I am logged in as a user with administrator
rights.
When I am logged in as a normal user, the command should
be available (was in the past)

Any help would be appreciated