It's a general error that is vague to say the least. Mostly it means there's something wrong with the format of your Mpeg. Important things to watch are the frame size, GOP size (no GOPs with greater than 15 Pictures), and especially the audio which must be 48 kHz not 44.1
Those are the most obvious things and less obvious and more or less invisible to the user are intrinsic parameters that are part of the encoding process, like pack size, and multiplexing rate.
In order of most common SpruceUp chokers.
1. GOP size problems
2. Audio rates
3. Errors in headers (ie PTS errors etc)
4. Broken GOPs
Sometimes, if you supply SpruceUp with elementary streams instead of program streams, you will have less trouble. Then SpruceUp does it's own multiplexing and can sometimes fix small problems. Many times, I've had SpruceUp choke on a multiplexed program stream, only to have it work perfectly after I demultiplexed the program stream into separate elementary streams. Ie. MyMovie.mpv for video and MyMovie.mpa for audio.