Thanks for posting!
It looks like the permissions are set correctly on the admin-console-client.jar file. Let's try clearing the java cache and launching the console again.
To do this, launch the Java Preferences application in /Applications/Utilities/, click on the Network tab and choose "Delete Files". Make sure that the Applications and Applets option is checked and then click Ok to clear the cache.
Once that's done, open your web browser, enter http://localhost:16000 in the address bar and click Start Admin Console.
Thanks for the reply.
I still get the same error "Admin Console could not start: Admin Server Manager unavailable."
I have installed the latest Java that I downloaded from FileMaker's website. The update was dated 14 March 2011.
The permissions are correct but there are extended attributes on admin-console-client.jar. Use ls -l@ to get a list of them and then remove each one using xattr -d attrname admin-console-client.jar.
I guess your problem is answered here: http://superuser.com/questions/28384/what-should-i-do-about-com-apple-quarantine
We reinstalled FileMaker Server instead. This fixed the problem we had.