Epson CX4800 in scan mode

Scanning at resolutions greater than 200 dpi causes an error message that says the computer cannot communicate with the scanner. This happens after some time into the scan. Epson is on USB 2.0.

There are also times, when printing, that the PC gets impatient with the HP laser printer, and messages that the document did not print, but it is still printing. HP is on ECP Centronics port.

I suspect that there is a timeout somewhere, but I don't know what to change. This is a home-built PC: ASUS mobo with AMD 2 GHz Athlon 64 X2, 667 MHz memory, XP Home Edition SP2.

The scan problem is lesser (I can use a higher resolution) when using a slower HP laptop.