This is a Tomcat problem. Search Google for Admin Server process has terminated abnormally. You are looking for a support page on the FileMaker web site which includes a shell script that fixes this problem. You could try searching filemaker site but I didn’t find it there until I went to google.
Thanks for the reply. I think we've isolated this to a problem with conflicting DNS settings between the System Preferences > Network and OS X Server > DNS Server (which was running locally).
Once the DNS system was able to resolve normally, everything (Admin Console, browser, etc.) seems to work much better. Funny how being connected to the network properly makes all the difference, even if connection is over localhost.
-- Drew Tenenholz