After search with different forum,
Here is what I found suspect:
in /opt/zimbra/logger/db/work, 2 files have a date of 11th december 2009 even if the server's date is 17th November 2009 !!!
zmlogprocess.state
zmlogprocess.optimize.state
during reboot after changing the UPS, I need to change date in bios but I could have make a mistake
I tried to stop logger and stats, remove this files and start them again, but date of this files come back to the 11th december 2009... unmess all other file created are at the right date.
Any idea ?