this "g-basic-rates 1 2 5 6 9 11 12" isn't really correct, it should just be "g-basic-rates 1 2" , given that you havent remove and rates from the g-tx-rates.
Start by changing that back to what it should be, "g-basic-rates 1 2" because I wonder if the change of AP (and radio chipset) has caused a change in the beacon rate. My suspicion right now is that it's now using the highest value (12Mbps) you have configured for beacons, whilst your symbol mc9050 is (i believe) only an 802.11b device, meaning it cannot decode beacons sent at 12Mbps, and this would match your symptoms.
Give that a go, if it still doesnt work, then there are some other things to do to isolate radio level interop (come back to this thread) but also check/do a driver upgrade on the mc9050 too if possible.
hth.