matt and shoe have a good point, check for interference...sunlight, cfl (from a plasma if you're using one), possible IR signals that are bouncing off of the screen/monitor wall back to the equipment that is probably facing the front of the room(if the client can read the displays). the bouncing IR wont be consistent, but it will mess with things sometimes. to stop that, i almost always use the Xantech IR mouse emitter sheilds (model MS1). i buy them by the hundreds, and they save me service call dollars by the hundreds...lol.