Could you guys clarify more exactly what devices are the clients ? I understand that they are iPad, iPhone 4 and Motorola Atrix, but please give also specific iOS version number and release date or serial. For apple devices you can use this link to get specific model number http://support.apple.com...

Set the rate-set=default and test again. Also how are the antennas aligned, we suggest to place on horizontal and one vertical? Could you check if the problem goes aways if you disable the power saving on the wireless clients? Rates set to default. I will sees if it happens again. It can take sever...

Another thread with the same problem on this model Mikrotik.

http://forum.mikrotik.com/viewtopic.php?f=7&t=68315

I'm waiting for mine to act up again with wireless debug on to see if it offers any more details.

I'm still having this problem with 5.24. Same model Mikrotik as well.

I get the "group key exchange timeout" in the log when it occurs and all wifi clients are unable to communicate for a few minutes before it resumes normal operation by itself.