GUI scripting question

First may I say that this site is Great I seem to always get my questions answered quickly and correctly.

I am trying to script Distiller so it will delete Watched Folders but I cannot get the script to select the 'Remove Folder" button. I keep getting this error message and it highlights the click button line in my script. “System Events got an error: NSReceiverEvaluationScriptError: 4” I am running 10.3.7 and Distiller 6.0.2.
Here is my script so far:

tell application “Acrobat Distiller 6.0.2”
end tell

tell application “System Events”
tell process “Acrobat Distiller 6.0”
keystroke “f” using command down – Watched Folders window
click button “Remove Folder” of window “Watched Folders”
end tell
end tell

Thank you for your help