Authentication before trashing

Hi,
I've got a Western Digital external hard drive connected to my PPC G5 running 10.5.8. When I drag an item from the drive to the trash, dialog box comes up that says "Finder requires that you type your password." This only happens when I'm trashing a file from the external hard drive and neither from the internal drives. My account is set as and admin, and I've checked keychain access. Any ideas how to make this stop?
Thanks
Michael

What are the permissions set to on the external drive?

Read and write. There are also 2 icons that say (unknown), 1 I can ste to read and write, the other will only let em set it to read only.