Was compressing videos of our family outings, then I started getting this error in FFmpeg. I was only able to fix the problem now, after a few months of anguishing over it.
I found out that the problem is with my anti-virus software, it's preventing the software from running. I disabled it temporarily to compress the files and now am trying to figure out how to white list this software. The program is clean because I downloaded it directly from the FFmpeg site and even scanned it with the AV software. Weird really, well at least I know my AV program is working.