You may need to uninstall everything Epson from your Mac (so that your old install is completely gone), then do NOT try to install anything from the installer CD that came with your CX3900.
You can download the Epson uninstaller (a current version) from here:
http://esupport.epson-europe.com/Pr...ZkGU002FaWywXyICw7bEoviZpquL2Zee8CAU003D&tc=6
You COULD also try the other installers on that same Epson page.
I think the Epson Scan app is still too old, BUT if that Epson Scan is removed, then that may allow the ViewScan software to control your scanner.
After running that Epson uninstaller, run the Epson install that you downloaded from Apple.
Finally, run the ViewScan install again.
Check to make sure that you can still print.
Open the ViewScan software, follow their setup, and test the scanner portion.
Another option to try: Attempt to scan while logged in to another user (If you don't yet have another user account, make a new user just for this purpose)
When you say "scanner still doesn't work", what exactly do you mean?
When you launch ScanView, does it detect the scanner? Or, does it tell you something like "no scanner found"
Or, does it try to use the scanner, but fails with an error of some kind?
Here's what I would do next: Boot to the Mountain Lion Repair system (Restart while holding Command-R), and reinstall OS X.
After that completes, run the Epson full install (the Apple download) again, and then the ViewScan again.
This _should_ work.