Model class categoryModelCategory not found in fil

I am getting the error message,"Model class categoryModelCategory not found in file" when I clcik on category menu on front-end after installing some extensions lately. The error is not preventing any issues there as I am able to access the categories and underlying products.

That error comes from the "front end user access" plugin:
www.hikashop.com/en/forum/4-how-to/35234...nd-in-fil.html#35234