I agree that it shouldn't create that error, which is why I'm confused by it.  According to ProSeries instructions, I was to create a backup to preserve the original return, then open the file and start making changes.  So I guess I did open the backed up file?  And no, I did not rename the amended file, which is what we usually do.  However, renaming the file doesn't change the fact that the SSN is a duplicate. I was trying to follow ProSeries instructions since e-filing these is new.