this._metaObject.getAttributeType(...) returns an object, so it has no function toLowerCase. Can it be that toLowerCase is wrongly used in an event-microflow of the datagrid's entity?
I had this issue too. I saw that some of the attributes of the entity shown in the grid (in my case in a search filter) didn't have read access for the user role that got this error. My clue was that this only happened with certain roles but not with others. I checked the access rights and saw that some attributes didn't have rights set where for the other roles all rights were properly set.
Maybe this helps.
It would make more sense if Mendix would throw a permissions error instead. But Mendix front end error don't always make much sense (^_^`)