According to these threads (via a google search of "AcceptSecurityContext error, data 525,"), it means a bad/unknown username:
http://forum.java.sun.com/thread.jspa?threadID=552621 http://forum.java.sun.com/thread.jspa?messageID=4227692
If you are using AD for authentication then there is no need to sync passwords to Zimbra, as it just uses AD for auth.