I had an unrelated problem with my Epson 4990, ended up calling Epson's tech support. The tech was very patient and helpful, but try as he and I might, we were unable to resolve the problem.
Nonetheless, my point is that the Epson tech tried everything he knew to do. I recommend you call Epson's tech support folks. They will do their best to solve your problem.
Oh, and apparently my problem lies either in the OS (Windows XP) or my USB hardware. The scanner works perfectly on another computer. Which reminds me, if you have another machine available, try the scanner on it, see what happens. If it works normally on the new machine, then it isn't the scanner.
Michael