It looks like your Asterisk is having problems with agent logins. If the agent is shown as logged in, it means that Asterisk did provide the "logged in" record, but likely something else is not working (and this is not a good sign).
I would do the following things:
a. move to a better version of Asterisk, or
b. restart Asterisk in a controlled way, eg.g. nightly, or
b. try and use ADDMEMBER instead of the AgentCallBack interface.