Xbee 2 and Change Detect

I’ve recently received my first xbees and I am currently just running some comm tests to fimiliarise myself with the commands. It’s an xbee series 2 connected to my PC via serial port with firmware 1320 in API mode. I can send commands like at%v, atd0 and atvr and get correct responses but when I try an atic command (I’ve set the DIO1 to Digital Input) I receive an “Invalid Command” response: -

Tx=7E 00 05 08 01 69 63 01 29

Rx=7E 00 05 88 01 69 63 02 A8

Can anybody suggest why this might be happening?