You may be experiencing an error when attempting to upload a song to BSaber.com.
Currently, Mediocre Mapper MK5 doesn’t conform to these new standards (read more about these here).
You will want to change to Mediocre Map Assistant.2. This is a fork of MK5 and has several additional enhancements as well as fixing this info.dat file fix.
I’ll be adding some parsing of the info.dat file to BMT to alert you of invalidity and offer a solution.