Seeing an error message in coursepress theme


I'm seeing this error message in this site: . This happens when I remove one or two texts from the course category URL. As you can see I deleted ty from productivity.
Also I see this error message on this site only. Other sites that have similar category url doesn't show this message when I do the same thing to its URL.

I just want to know what does this error message mean?
A solution would be ideal but if it takes too much of a work I would neglect it. Chances of someone doing these sort of a thing is very minimum :slight_smile: