I have RB433AH and CM9 card in AP mode (RouterOS 6.6). On AP there are 25 clients. First, card was in g-only mode, most of clients have 100% ccq, 54/54Mbps rate, but some of clients has same rate and ccq but distance show 30-40km???.(farthest client is 2km from antenna with clear sight). From time to time i got complains from clients that they cant ping anything. I checked ping from AP to client and the result was 2000-3000ms??? Then i changed freq and ping is now 1-2ms. After day or two same thing, i returned freq that was before i changed first time and again ping is 1-2ms. Now card is in b mode, rate is 11/11, ccq 100%, distance 1-3km, this setting worked 3 days after i need to change freq again...This AP is only in area.
So, ccq and signal are ok but ping goes to 2-3000ms. Antenna is http://www.rfhamdesign.com/images/slott ... 13cm02.jpg. I spoke with some people and they said that problem is maybe in antenna??? I dont think so i ask you guys! Can you help me?

First suggestion would be to do a wireless interface configuration reset, here is an example of the command:
/interface wireless reset-configuration wlan1

Then configure the settings you only need. If your clients are not very far (up to few km) then you could try to set the distance value to indoors and check if it works fine after few days.

First suggestion would be to do a wireless interface configuration reset, here is an example of the command:
/interface wireless reset-configuration wlan1

Then configure the settings you only need. If your clients are not very far (up to few km) then you could try to set the distance value to indoors and check if it works fine after few days.

I reset configuration and set indoors. Worked till now. Again same problem, some of clients keep connect/disconnect, others ping 2000ms....

maybe you are experiencing hidden-node issue and that is why you start to see the latency issues.
If it it possible try to enable the RTS/CTS option on the clients.
If not possible to do that, try to enable the cts-to-self hw-protection-mode on the AP and check if that helps.
Also I would suggest to look for a client that experiences the most of the wireless retransmissions as that client could effect the whole AP.

80211 b/g ap can suffer like this if just one client is using high upload. Torrent seeding is a big killer. If poss switch to a tdma protocol. Nstream or nv2