NOTE: You can also launch the uninstaller from the following location:
/Library/Application Support/FileMaker/FileMaker Server/FMS 12 Uninstaller.app
Also includes this warning:
Clear the Java cache and web browser cache
Even after you uninstall FileMaker Server, the Java cache may retain pointers to FileMaker Server components that have been uninstalled. In addition, your web browser may retain cached versions of artwork and HTML files that have been uninstalled.
And of course, reboot when you're done.
Can you not access the uninstaller app from the above location?