Bill,
I too had a hard time programing the codes of my ProScan DSS remote and was about to give up but then I tried something different. The Pronto would give me the FAILED sound almost immediately after I pressed the button on the ProScan remote so I knew it was getting something it didn't like. I then placed the remotes about two feet apart (instead of the usual 4-8 inches)on a table and bingo, this did the trick.

I hope this works fo you as well.