Trying to delete files... not working.

[dataflux]

I'm using the copy action to delete files. I want to delete all files ending in .complete from all of the subdirectories of the specified directory. In the copy tab of my properties, I have left the Source Folder empty, and specified the root of the target directory in Dest folder. In the include list, I have one line which is *.complete. In the check boxes at the bottom, everything is unchecked except Delete destination files and folders... Everything else in this action is default.
When I run this action, I get:
Source Folder cannot be empty
Step 'Delete .complete files' failed

Any ideas?