There is also an AB fix that worked for me. I had a spare ecu to plug in, I did it with the wires hanging out and everything worked fine. By the time I got it all back together, the rear windows stopped working again. I did this bypass and they work all the time now. Same as posted above. You do not have to buy the wire from them...
Fix A Relay Failure Problem With The Window Lift ECU
How to fix a relay failure problem with the Window Lift ECU resulting in loss of control of the rear windows.
www.roverparts.com