This is the result of using the Save As command repeatedly. Save As should be used only when you want to rename the file or save it to another location. If you're saving your script as a matter of practice during a writing session, use the Save command rather than the Save As command.
The remedy to this problem is just what the error message states, which is to save the file with a different name or to a different place. Once that's done, do not use the Save As command unless you intend to create another copy.
IMPORTANT: Live technical support (phone, chat, email) for Final Draft 8 will end on December 31, 2017. You will still be able to find information and solutions in this knowledge base, in the online troubleshooter and in the FD8 User Guide.
NOTE: All support for Final Draft 7, including software activation, has been discontinued. You may find solutions to problems in the online knowledge base or in the PDF manual found on the installation CD.