This doesn't work?
if arcpy.Exists(your_output):
arcpy.Delete_management(your_output)
Nope. That was the first thing I tried. I also tried the following to try to get at this without going through arcpy:import os
if os.path.exists(your_output):
os.remove(your_output)
The problem is that the error is thrown before the script even executes so there is nothing I can add to the script to fix it. Seems to be a validation issue. I'm going to try deleting the tool GUI and starting from scratch.Brent