Basically, you are trying to accomplish a calculation that you are wanting to do sum of data on and the calculation can't do it. Usually, this means you are missing a Top Level member of a list (which is used to get a total of that list).
For example, if I have a list of Employee's without a top member,
Well, there is nothing at the top to sum that data. To fix that, put in.a top level member in the Configure tab of the list All Employees