Will not driving an A4 cause transmission problems
 

I have a 2006 Audi A4 that's just been sitting in the garage for about 5 or 6 months. It was my wife car until she got her new one. The other day I had it out going around town and it drives great. Left a store put it in reverse and nothing happened, it just rev'd like it was in neutral, checked the dash cluster and the square wasn't around the R. Put it back in park turned it off, turned it back on and reverse worked fine. Then drove it fine for 2 days, then the reverse problem happened again. No warning light, no weird noises, no nothing. The last thing that was done to the car before my wife got her new one was we had the ecu emc computer changed. Took it to the Audi dealership and they said pretty much with no warning lights they couldn't do anything but if he had to guess it would be the reverse band in the tranny. I had a local mechanic check the tranny fluid and that all checked out fine. I also heard from the local mechanic that it could be the transmission selenoid. Just looking for thoughts before i have them break down the tranny and find out it wasn't that. thanks. Could the ecu computer have gone bad again, maybe a wiring problem