I've found Yet Another Cause of the bug where the "Server Status" is not available in the Admin console:a pid file was corrupted.

A console capture below pretty much tells the tale. I restarted Zimbra and it seems to work now.

Note that there have been no migrations done on this server but there have been many Zimbra upgrades applied in the usual (normal) manner. There were also a couple of system crashes last year too, though I can't remember when.

Code:
root@zimbra:~# ls -l /tmp
total 20
drwx------ 2 alf    alf    4096 2012-03-04 07:35 gconfd-alf
drwxr-x--- 2 root   root   4096 2012-03-04 15:05 hsperfdata_root
drwxr-x--- 2 zimbra zimbra 4096 2012-03-04 15:05 hsperfdata_zimbra
-rw-r--r-- 1 zimbra zimbra  148 2012-03-04 15:00 logprocess.out
drwx------ 2 alf    alf    4096 2012-03-04 07:35 orbit-alf
-rw------- 1 root   root      0 2012-03-03 08:23 tmp.InipwT5417
root@zimbra:~# cat /tmp/logprocess.out
Argument "spell" isn't numeric in kill at /opt/zimbra/libexec/zmlogprocess line 74.
/opt/zimbra/libexec/zmlogprocess already running with pid spell
root@zimbra:~# ls -l /opt/zimbra/log/zmlogprocess.pid
-rw-r--r-- 1 zimbra zimbra 5 2011-08-01 13:00 /opt/zimbra/log/zmlogprocess.pid
root@zimbra:~# cat /opt/zimbra/log/zmlogprocess.pid
spellroot@zimbra:~# mv -i /opt/zimbra/log/zmlogprocess.pid /opt/zimbra/log/zmlogprocess.pid.bogus
root@zimbra:~#