CAPs losing connection to CAPsMAN

Hi,

I have here about 70 AP’s with RouterOS v6.40.4. Most of time 5-10 of them are missing in CAPsMAN and not forwarding any data. On WebUI of the AP’s “WebFig” (if reachable) all Menues are empty. No interfacies, nothing.
With Telnet, I can connect to the AP and see in Logs “snmp,warning timeout while waiting for program 20”. When I reboot from console, the AP works for short time.

What the devil is “program 20” where the AP is waiting for?

Regards,
kjaeger