Just updated with the security update 2012-002 and cannot log on to server?

So you have no login access whatsoever?

Using Target Disk Mode to gain access to the log files (from another OS X system) will give you a look at what's in the log files. How Target Disk Mode is cabled and established varies (somewhat) by which particular Mac box is involved, and is also obviously dependent on whether you have a second Mac with a matching I/O port.

But then, rolling in your backups will probably be the fastest way back to operational status.