Dsum not working- invalid use of null

[ozdemirozgur]

My Dsum function is not working but seems nothing wrong with the null data.

DSum("[NumofRoom]", "RoomDetails", "[RoomId] = 'Main!Id' and [Pos] = 'D' and [Year] = 2000"))

 

[RuralGuy]

Try:
DSum("[NumofRoom]", "RoomDetails", "[RoomId] = '" & Id & "' and [Pos] = 'D' and [Year] = 2000"))