Unknown Error - Anyone know how to fix this?

On both the 3.1 and 3.1.1 beta release I am getting this unknown error message when I try to process a preview. I tried reinstalling the application from scratch but that did not fix the problem. Anyone know what I can do to fix this?

Last FFmpeg messages:

Unable to parse option value “0” as video rate

Unable to parse option value “0” as video rate