If the name of any path or file involved in the conversion contains any characters other than letters and numbers (such as spaces, dashes, or underscores), rename the path or move the file to eliminate them; see §1.1.2 File, directory, and path names. FrameMaker does not handle spaces in file names very well; Mif2Go does not care.
If all file and path names are free of non-alphanumeric characters and your conversion is still not producing any output, check whether any of your FrameMaker files are on a network drive. FrameMaker is noted for not running properly when files are on a network drive. (Mif2Go does not care what sort of drive you use.) Move your FrameMaker files to a local drive and try again.
File names and paths valid, and the problem still exists? Next: Check for file corruption.