Whoops!! You specified a position that has not been allocated. Please create a row/column before using it.
The formula is attempting to retrieve data from a cell that is outside the range of the current data window. If you are using the index() command within the cell() command (for example, cell(index(), 2) = cell(index(), 1) + cell(index()+1, 1)), you may need to make an appropriate selection in the data window before running the formula to avoid getting the error.