Sanwa M11x problem

[h0m3sy]

Im having trouble changing the modulation type or channel mode to 2 channel . The manual states 1) press the ENTER key to move the cursor to CHANNEL, then press the INC/+ or DEC/- keys to set the desired channel mode. The trouble is that when I press the inc or dec button, the display reads..Display Mode Only. This is driving me mad, it's probably an easy fix. Can someone please tell me where I have went or I'm going wrong .