I note in mailbox.log of some 7.2.0 this error

2012-09-12 08:28:00,150 INFO [btpool0-17117://zimbra.xxxxx.com/service/spnego] [ip=;ua=Zimbra-ZCO/ (6.1.7601 Service Pack 1;; it-IT);] account - spnego auth failed: system failure: no spnego user realm
These errors happen with external auth, AD and LDap.

I argue (maye I am wrong) that password was changed in windows and such account are reading mail using mobile devices or connected by other company branches, so the connected outlook in main branch (pc's are let always on...) complains and gives this error