xbee series 2 modules are not communicating

hi

im using xbee series 2modules im trying to establish communicaton between them through xctu software,iam unable to chang the frimware to zigbee coordinatorAT from zigbee router/end device.its showing an error message like in com[atable function set selected

lost communication with modem

unable to write the write parameters

pls help me

do you intend to run a mesh and thus need ZigBee versus the other firmware option: wireless serial port extension?

hi im sorry to say this im not able to understand what excatly u want to know from me