General :: Run A Command With The 'at' Scheduler In Mint 9?

I'm trying to run a command with the 'at' scheduler in Linux Mint 9. It's basically a ssh connection to my Smoothwall firewall to tell it to shut down, but that part isn't really important. The problem I have is that I can't get the 'at' schedule command to do much. I can type commands into the terminal and they work perfectly. If I enter exactly the same command into 'at' nothing happens.

For example, I can type 'plink -load smoothwall' into a terminal and a new ssh terminal comes up asking for my password to make an ssh connection. If I create an 'at' job with the same command, ie:

Code:
$ at now + 5 minutes
at> plink -load smoothwall
at> <Ctrl-d>
$

then nothing at all happens when the 5 minutes are up. I've checked that the job exists by doing an 'atq' command. Obviously there's something about 'at' that I don't understand. I've googled, I've looked in this forum and I've looked in a copy of 'The Linux Bible 2010' all without success. I've tried various alternative ways of entering the command for a couple of hours and I'm still stuck.