It might be the server.pem file.
For More Information see: FMP installer does not install server.pem file
This is one of many acknowledged bugs that can be found in the Known Bug List thread here in the Report an Issue section of the forum.
It can also be downloaded as a database file from: https://www.dropbox.com/s/jt09b82i0xijbu3/FMP%20Bugs.zip
We currently have two computers with FM12 installed and both are having the same problem so what do I do if I don't have a machine with a working server.pem file? Would uninstalling and reinstalling fix the problem?
It might. Since this is a recent purchase, you might also try calling tech support to see what they say. They don't charge for support for installation issues and might class this one as such.
Also check the documentation to confirm that you have the correct ports open.
We finally did get it working then. Turned out it was the TCP port. Grrr... I thought I had checked that before. Thanks for all you help anyway. :-)