Final Draft v.7 is not supported on Mac OS X 10.8 (Mountain Lion) or 10.7 (Lion), it's too old. If you need to run Final Draft on a computer with one of these operating systems, you will want to upgrade to v.8, which was designed for 10.8 / 10.7.
If you're on OS X 10.6.8 or older: The problem may be the result of a problem with FD 7.1.2 and Mac OS X's File Vault. This problem was eliminated with the 7.1.3 update, available HERE.
NOTE: Although Final Draft 7 runs fine in all other regards with File Vault on, adding words to the User Dictionary is non-functional. If you need to add words to the User Dictionary, you will have to turn File Vault off (Apple Menu/System Preferences/Security).