receiving uknown information from xbee's connected to atmega16 MCU.

hai, i am working on a project in which three Xbees are to be connected to robots having atmega16 microcontrollers. three Xbees are configured with same channel and panid so for testing process i have connected one Xbee to pc and other two to the micro controllers. now when i transmit number 8 from XCTU when any one robot is off i am receiving the next number that is 9, for 9 i receive : (colon) and when both the robots are ON I receive continuous unknown symbols and numbers.