It's possible that you've encountered a Known Issue. For More Information see: Records with a PDF file linked to an active container field cause FMP 12 to crash in OS 10.9
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
There's a fix described in this thread.
If your situation does not match this issue, please post an Issue Report over in Report and Issue to bring this to the attention of the TS personnel that monitor that part of this forum.