Final Cut Pro X Crashes when sending to device

Hey, so I'm trying to get the movies I'm creating to be .mp4 so I can put it on my phone. However, everytime I go to Share>Apple Devices, Final Cut glitches. It begins to render the movie but then freezes at the "Processing" stage of rendering. The message I get is that FCP "generated an error or unexpectedly quit". This feature was working perfectly yesterday too. Is there a way for me to fix this? Or perhaps there is another way to get .mp4 on FCPX?