XBEE ZB End Device not joining network

, ,

I have 3 nos of XBEE PRO S2 radios. I have configured them as coordinator, router and end device respectively by changing their firmware using X-CTU.

Coordinator: XBP24-ZB, 21A7, API2
Router: XBP24-ZB, 23A7, API2
End Device: XBP24-ZB, 29A7, API2

ID, SC, ZS, Security n all necessary parameters are same for all three.
For Coordinator & Router joining is permitted.
Coordinator and router is connected with good LQI on both side (255/255).
End device is not joining the network.
Coordinator ā€”> End Device LQI: 255
End Device ----> Coordinator LQI: ??

Iā€™m really stuck with this. Could anyone help me out?