75: Invalid notes markup

You started a block with three underscores ___, which mark notes. The first line of a notes block may not contain anything apart from the underscores. In your case the underscores are followed by other characters within the same line.

Solution

Make sure that the first line of your notes block contains nothing but underscores. Here is a valid example that explains the meaning of a few physical symbols in a tagged list as a note:

___
<kg> kilogram, base unit of mass
<m>  meter, base unit of length
<s>  second, base unit of time

If you did not mean to create notes but want to use three underscores at the start of a paragraph, you can prepend all underscores with backslashes: \_\_\_. Mind that if you prepend these partially, the underscores without a leading backslash will be interpreted as marks for supplementary emphasis.