Twain Error Connecting to Scanner


I have an Epson Stylus Photo RX500 (an "all-in-one") connected by USB to a Mac G4 running Mac OS 10.3.9. It has been working for many months. Now, when I try to connect to the scanner, I get an error from the Epson application that it "Cannot open TWAIN." The maddening part is, I can see the TWAIN files installed; of course, I have no idea if something is missing or corrupt. I reinstalled the Epson software disk but it didn't solve the problem. I moved the USB to the back USB port (instead of the extension hub). I restarted the computer and the Epson machine. If I assume some TWAIN related software is missing, what would it be, where should it be located? Thanks!
Epson got back to me with the standard instructions for quick and also complete methods for uninstalling the software, for a complete reinstall. This solved the problem.