Before it was cisco AP, everything worked fine except speed, cause 16 clients hanged on it. Now there is routerboard 532, cm9 2.4 GHz, same 15DB omni. Some clients cannot connect at all. Clients have MT routers with cisco pc cards, d-links and linksys. Just 8-9 clients are working normally. I cannot understand where might be the problem. 
do u have mt 2.9.8 ??
yeah, I have tried also 2.9.6 and 2.9.7
are you running auto b/g ?
sometimes causes problems … try g or b only.
Regards
Have tried both b/g and only b! Maybe because of power? cm9 has 65 mW and cisco 350 has 100mW.
I have the same problem. We have JAHT and TrendNet TEW-210APB wireless access point working as clients. They cannot connect to MT 512 using version 2.9.8.
Other APs, like Pheenet, SmartBridges or TrendNET TEW-410APB+ connects and works fine.
The difference i’ve noticed between these APs, that pheenets and smartbridges hides PC mac-address. I think it is called proxy ARP.
Any suggestions?
Just upgrade the firmware of the TEW-210APB!