Thanks for the idea Wrex, but that wasn't it. It was the Schedule service's requirement for local Administrator access rights. I am using the /interactive switch though, as I like to see the Perl activity happen in a CMD window. I was recently caught out by running a PERL script that opened a file but had an error and was waiting for me hit return before altering the file and closing it. I mistakenly called the script via the AT command, without the /interactive switch, and couldn't for the life of me work out why the file was always locked and the script would not run again unless I rebooted. The script was waiting, invisibly, for me to hit return. I now never call a Perl script via AT without the /interactive switch unless I am POSITIVE that it is bug-free.