As you are able to display the ALV grid, execute the Consistency Check, that will display in-consistency errors between the internal table fields names and content of structures like the field catalog or the layout.
One of most frequent beginner's error is the affectation of the BOX field to the internal table (often after copy of other's sources), also when you change a structure in development, use report BALVBUFDEL to reset ALV buffers.
Regards,
Raymond