I have the same problem, FOP2 2.26 crash frequently with this error:

"Payload is too big. Deny big message (3438024762989167196) or increase max_payload_size (65536) at script/fop2_server.pl line 1712."

I have already set "true" for "disableWebSocket" in presence.js but the problem is still present:

var disableWebSocket = true;

I've tried to upgrade to FOP2 2.27 but this version (http://download.fop2.com/fop2-2.27-centos-x86_64.tgz) doesn't accept the registration code, I can't try it unregistered because for me is essential the address book feature.

What can I do?