98: Incomplete custom mark

An ampersand & is used for custom marks in the text. A custom mark consists of the ampersand, immediately followed by a small or capital letter, az or AZ, or a single digit 09. In your case, a character after the ampersand is missing.

Solution

Make sure that the ampersand is immediately followed by a letter or digit, if you want to use a custom mark. If you do not want to use a custom mark, but want a regular ampersand instead, you can prepend a backslash: \&