Not able to call local ext

Hi, Every one , i had an old Freepbx in which i had installed asterisk 1.2,zaptel 1.2,freepbx 2.4, etc its working fine my problem is i had configured an new PBX in my new office and installed all the latest versions such as asterisk 1.4,zaptel 1.4,freepbx 2.6 etc all latest ,
my problem is i am able to call my local ext from new pbx to old pbx its working fine and i am not able to call from old pbx to new pbx its telling channel unavilable
how to solve it