Implication of USB is "wired USB" but I share what I do in case it is "wireless USB" via a dongle on the end of a USB cable and in case anyone else with the latter finds this thread in the future.
I had a similar problem last year; occasional incorrect characters (and occasionally no characters).
The cause was my digital cordless telephone handset sitting on its base station next to the wireless keyboard dongle.
Moving the telephone a foot apart from the keyboard dongle solved the problem.
Same frequency contention and same solution for the wireless doorbell in the kitchen; it didn't always ring when the kitchen telephone base station was adjacent to it.
Last edited by The late XV105; 27th September 2011 at 11:47.