Xbee startup probs

After hours of strugling I finally managed to connect both of my xBee modules to x-ctu using Arduino. When I press the read button the read performs correctly. (version 10CD). When I press write with the settings I just read I get the following:

Getting modem type....OK
Programming modem...Lost communication with modem
Write Parameters...Failed

The "inserting module after pressing write" did not work for me too. Does anybody know where the problem is, would appreciate the help.
Thanks,

What kind of XBees do you have? Series 1 or 2.5? Pro or regular?