automator "copy finder items" broken

I have an Automator script that ran fine under all versions of Tiger but it's broken under Leopard. It is a simple script that copies a few files from my main hard drive to a thumb drive. The relevant steps are

1. Get Specified Finder Items
2. Copy Finder Items (replace existing files) {to a USB thumb drive}

Step 2 breaks with the very helpful notice
The action "Copy Finder Items" encountered an error.

I've run this little backup script many, many times with no problems.