I just got Update Manager installed in my vCenter 5.1 install. I have a few 5.0 esxi and a single esxi 4.0. I was trying to stage updates to the 4.0 host, but the small 500MB /var/tmp/cache (on / partition) is too small. So, I changed in the conf file (/etc/vmware/esxupdate/esxupdate.conf) the location of the temp to be one of the datastore mounts that has lots of free space. I then try to redo the stage, and it failed with error 16, failed to parse config. I look at the config now, and it's completely empty, 0 bytes. I'm dead in the water. This was the only 4.0 system I have, so no way to look at another.
If you have an ESXi 4.0 system, and can please paste the content of that file here, that would get me back up and running. I've checked the 5.0 systems, and they don't seem to have this file. (found one, but the content looks different, and it's in a different location)