I bought this Samsung SCX-4200 printer/copier/scanner early this year. The printing and copying function work fine. At its price, it seems to be a good investment. Since we have another old Acer S2W 3300U and it works very well so we have not used the scanning function. But the first time we tried to use it, it gave us "Hardware I/O error". I have tried it under three different PCs, under Windows Vista, XP and Ubuntu Linux. All have the same error even though it works fine as a printer under all three OS. So I was thinking to call Samsung coming Monday since it is still under Warranty.
Today I read this solution here. Finally I understand the problem. The problem seems to be that the scanner does not work fine
Under Linux, one can rmmod the EHCI driver (high speed USB) to force it to use Full Speed USB transfer. Under Windows, my solution is to put a USB 1.1 Hub in between. After that, the scanner works fine.