The Error "Relate, Compute By, and Sort operations cannot be performed on column(s) whose defined size is unknown or too large." appears when running a report/query in the Scheduler. 

This error can arise when a scheduled report is run where an filed in the sort orders, ( i.e, used in a group by of a report )  is set to a value larger than 254

The current Work-around is to change the value in the Analytics Engine , then remove and re-add the columns to the thew query.