Applescript to Eject Disk has stopped working

My computer has two internal IDE diskdrives, of which I use one for backup. Before updating to 10.4.6, I had an applescript run as a login item which would eject the back-up drive (tell application "Finder", eject "disk name", end tell). Since updating to 10.4.6 from 10.2.8 this applescript no longer works. I have also created an automator script which consists of "Get selected finder items" followed by "Eject Disk" which also doesn't work.

When I try to eject the disk by dragging it to the trash, or using Disk Utility, I am prompted to authenticate with my system password. I believe this authentication is stopping the scripted ejection of the disk. Any ideas why it is now asking for authentication, and how to work around it, or stop it from asking for a password?

Thanks!