As of Java 7 update 51 (7u51), there is a requirement for a new Permissions attribute (introduced in 7u25) that prevents the FileMaker Server 12 Admin Console from running. This also affects the version 11, 10, and 9 Admin Console and probably other FileMaker products utilizing Java.
After a warning that the application will be blocked by future versions of Java you get a generic "Application Error" declaring that Java was "Unable to launch the application.". Diving into the details will turn up the precise reason as:
Missing required Permissions manifest attribute in main jar: http://fm-server:16000/admin-client-lib/admin-console-client.jar.
FMS 12 is updated to the latest version at this time and the Permissions attribute has not been added to the Admin Console jar by FileMaker, Inc.
Best Answer
To launch the FileMaker Server Admin Console, you will need to make a modification to your Java security settings. The originating web address of the Admin Console download needs to be whitelisted.
Open the Java Control Panel and navigate to the Security tab. Click the "Edit Site List" button. Add the FileMaker Server web address including the port and http:
http://your-fm-server-address:16000. Ignore the warning about insecure HTTP that pops up.You can now launch the FileMaker Server Admin Console by acknowledging the warnings at run time.
EDIT: Although the FileMaker Server internal web start page and Admin Console say there are no updates available, 12.0.5(12.0v5 is available from the FileMaker, Inc. website and claims to have a fix for the Java security issue. http://help.filemaker.com/app/answers/detail/a_id/12826/~/software-update%3A-filemaker-server-12.0v5-and-filemaker-server-12.0v5-advanced