@Dennis ...
Might be confusing cause there is more than a single issue with the error - so depends on factors.
In my case ... courses in Spanish (actually ALL Language courses) ... section labels were set to Custom but there was no text in Section Title entered. Thought that using Custom required something to be entered but it did not. Teachers were using blank Custom Section Titles for a 'better viewing experience' ... or so I was told. Or language characters (could see them in DB records - machine language characters - and not the special characters for that language ... that caused the issues. All needed language packs installed ... fr, spanish, etc. Soooo ?????
So suggest checking the course .. in particular settings for Section headings.
'SoS', Ken