ffmpeg not converting files from mkv to mp4 with encoder: Lavf55.12.0?

Question

fmpeg

I do this:
ffmpeg -i "film.mkv" -strict experimental film.mp4
I get this:

[matroska,webm @ 0x29fb0e0] Read error at pos. 93417 (0x16ce9)

the video file itself plays and everything is ok, but when I try to convert it gives out ... and other files with the same extension are normally converted
for this file by encoder: Lavf55.12.0 - for other mkv files that do not have it, it normally converts. ..
but I'm not sure about this - whether or not ... how to fix this at all?