EnderElemental, where did you get that ffmpeg version from? It seems like it wasn't build with support for the libx264 codec, so you won't be able to use MP4 as a export format (actually it seems like it doesn't support any codecs at all). Try to install ffmpeg from their official site, those builds should have support for libx264.
Poquito, your log isn't quite complete, the error is missing. Your issue is not the same one as EnderElemental's (your output shows that libx264 was enabled in your build: --enable-libx264
).
--enable-libx264
).