Yeah I dealt with the same error. I disabled ads and renabled it, however this also clear it well partially, sometimes there will be a remnant of an old ad. When this happened to me though I was between creating categories and kept deleting and creating new, because I could not decide. How I plan to utilize ads being the list doesnot work l with a collapse tree or anything more condensed at moment, is making data lists and fields for different category sections that are also searchable. Huge undertaking though. So if you did not add anything it probably was doing what I did. I had a ton of categories added and was switching them and adding. Should have maybe cleared cache between.