I am using the loopback test described in your web site - http://ftp1.digi.com/support/documentation/90001067_a.pdf (2 XBEE PRO S2B) (Sparkfun connected to PC - configured as ZIGBEE COORDINATOR AT <>  other platform board configured as out of the box) The Associate pin on  blinks after a short bootup, but a loopback test per the reference times out. The ATND command issued from X-CTU initially produced the requisite output but now produces a blank line. Is repeating signal on the “Associate pin” a sign of communication between devices? Thanks
Try shorting data in to data out on the remote module. Then set the data receive timeout in the range test to 5 seconds.