Xtend module with microcontroller

I have been trying to controll my xtend module with atmega 128 (avr) microcontroller. As datasheet would say i connected DI to TX pin of my controller DO to RX and common ground. Now what i did was i send continuously with delay of 1 sec a word. MY reciever end is another module connected to terminal of X-CTU. at first i got it all right. X-CTU recieved data that i was sending but after about 90 bytes it stopped never to be detected again.

What could be the problem?? Could anyone help. I used module in default configuration.

Did you remember to connect the Shut Down pin?