0 bytes avil file in flash card

I got a trail cam i leave every night on my hunting spot. When i pick the flahs card i use to record the videos captured during the night, sometimes i find 0 byte avi files, mixed with good ones, for instance, last night 10 avis were captures, from 1 to 3 all ok, from 4 to 7 i got 0 byte files and from 8 to 10 are okay too. This is so strange.

I guess this can be some missing pointer or anything? So ive been thinking that its possible the files are actually on the flash memory but its the file header or pointer not working.

Im reading the flash memory from Windows 7.