This is usually caused by an illegal HTML character in one of the comments.

You can remove illegal characters by copying the text of a comment, pasting the text into Notepad or another plain-text editor, and then copying the text and pasting it back into the comment.

You can determine which comment is causing a problem by generating the report, and moving the end date back. When the report generates correctly, that indicates that one of the comments immediately following the end date is causing the issue.