According to your description, your topology is as below, right?
Omnitik(Access point))))))))))((((((((((CPE510(Bridge mode)——2nd AP)))))))

1. What's your firmware version? Upgrade it to latest and retry.
2. What's your meaning of "I'm doing ping from AP Omnitik to CPE"? You use a ping tool in Omnitik? Or you mean use a PC in front of Omnitik?
3. Which mode does Omnitik works in? Bridging or routing as below link?
http://routerboard.com/RBOmnitikUPA-5HnD
If it is in routing and you want to PING CPE510 from WAN port, port forwarding is needed. And for remotely login in CPE510, you should navigate to Management tab in the web-based UI and configure the Web Server correctly.

1. What's the mode on your CPE510 (client or bridge)?
2. Did you enable WDS on CPE510 under wireless menu, if so, try to disable WDS.
3. Try with this new beta: http://forum.tp-link.com/showthread.php?83955-TP_PharOS_1.3.3_151112_Beta-fix-WPA-PSK-and-CDP-issue-with-Mikrotik-add-management-VLAN

already upgrade with beta fw following your link, now is getting worst

ping is can solve from my omnitik latency is very good, but from cpe510 is very worst almost thousand and can't connect to internet

power also max set only 23dbm and rx not stable can reach 130 mbps but suddenly drop to 6 mbps, thats way connection from cpe side is not stable

i just test this equipment only 10 meters

Temporary solved for internet connection
I change back to 1.1 FW, but previous problem still have
I can't direct ping from omnitik side......, but internet can connect ......
Omnitik is ap bridge mode & cpe also bridge...., supposed there is no problem

looking forward from admin to solve this issue,.... this is because of firmware

Although you are unlikely to make the below mistakes but I want to confirm:
What's the IP address of the devices? As I know, Omnitik's ip is 192.168.88.x network segment, and CPE510 with static ip address 192.168.0.254. If they are not in the same network segment, it's normal that CPE couldn't be ping.

You connect your CPE510 to 2nd AP though wireless or wired network cable?

Have you tried the WDS disable/enable thing? What's the result? It could be a problem.

Not sure the exact problem you have met with the new firmware:
CPE510 even can't connect to Omnitik,no internet to 2nd AP?
Both the 2nd AP and CPE510 failed to ping Omnitik when you use new firmware?
What do you mean by ' ping is can solve from my omnitik latency is very good, but from cpe510 is very worst almost thousand and can't connect to internet'? Do you mean you can use ominiTik to ping cpe510 with a low latency, while you failed use cpe510 to ping ominitik? That's strange......

IP address off course in in segment, I also use omnitik with rb433 as a bridge and don't have this issueI'd tried use wds and disable it, in wds mode this CPE can't connecting.My meaning when I had upgrade firmware to latest , the problem that's found before can solved ( already can ping from omnitik to CPE ), but another problem come outInternet can't connect and also ping to CPE is very high around 5. - 2000 ms without load any data.So I had back to original firmware 1.1Internet connection becoming OK and ping also stable at 2ms, but same problem I can't ping to my CPE from omnitik side, At the same time ping to another devices those connected to omnituk, there is no problem.And why when using latest firmware the power dBm only max at 23dbmAnd tx Rx can drop suddenly from 130mbps to 6 mpbs, not stableThis kind of problem maybe effected to internet accessI already bought 2 PCs, and had this kind of problemComparing with another brand and no problem.I'm almost 6 years is doing small ISP , and need to settle this issue

1. Enable WDS, your 2nd AP can access internet while can't ping CPE; Disable WDS, your 2nd AP can access internet and can also ping CPE, is it right? If so, why not just disable WDS?

2. When you change the new beta, as you said it's working, there might be some other changes to lead the drop 130mbps to 6 mpbs. Did you change anything after upgrade to the new beta, like CPE's position, channel, etc? What't the signal strength showed on the status menu of CPE510? Make sure they have a good wireless connection at first.

3. For the 23dBm change, it has already been changed from previous firmware version 1.2.1, just display changed, the actually output power hasn't been changed, refer to: http://forum.tp-link.com/showthread.php?81152-TP-PharOS-1.2.1-on-CPE510-Max-Transmit-Power-is-23-dBm-not-27-dBm

4. Actually V1.1 is too old, many new beta or official version has been released. http://www.tp-link.com/en/download/CPE510_V1.html#Firmware