Thank you for your post.
I have FileMaker Pro 12 installed and running on my Mac OS X 10.10.1 iMac. I suspect that the initial download for FileMaker Pro 12 was incomplete, so I would first remove all instances of FileMaker Pro 12 from your machine, and then download a fresh copy of FileMaker Pro 12. After downloading, then install FileMaker Pro 12.
If you still have difficulty installing FileMaker Pro 12, please contact our Technical Support department. If you are located in North America, call toll-free 800-325-2747. You will not be charged for installation issues. If you are located outside of North America, contact the FileMaker office nearest you.