There can be several possible causes for this problem.  One possibility is that the robot and host are running different versions of software, and another common problem is radio interference from another source.
 
Just to start isolating problems, download the firmware loader software - LPC21ISP.EXE - from our website -  
    http://www.surveyor.com/srvdownload/lpc21isp.exe
 
Also, download the latest version of firmware - srv1.hex.092706 - and rename it to srv1.hex -
    http://www.surveyor.com/srvdownload/srv1.hex.092706
 
Make certain that lpc21isp and srv1.hex are in the same directory.  Start a DOS console (Run Cmd), and change directory to the location of lpc21isp and srv1.hex.  Turn off the robot power, then start the following:
 
>   lpc21isp -termonly -hex srv1.hex com4 112400 14746
 
change "com4" to whatever com port has been assigned to the USB radio
 
Then start the robot power, and please indicate what information, if any, appears in the DOS console.

Okay - it seems that the radio and the robot are working, but there are 2 problems :
 
1.  the radio should be running modem firmware version 1090, not 106.  I don't know how this could happen, as we test the configuration of all radios before we ship, but perhaps the radio got reset somehow.  In any case, you will need to run the X-CTU XBee configuration utility after downloading v1090 from http://www.surveyor.com/srvdownload/xbee_v1090.zip , then in the modem configuration section, Get New Firmware from File, and point to xbee_v1090.zip.  In the modem configuration section, select XBP24, non-beacon, firmware version 1090, then make certain the baud rate is set to 115200 (option 7) and that the radio power is set to either 2 or 4.  Then write the modem configuration.  Make certain that both radios (robot and USB radio) have the v1090.
 
2.  once the radios are properly configured, you need to update the robot firmware to the 092709 version.  Before starting LPC21ISP, make certain you have to 092706 version of srv1.hex in the same directory with LPC21ISP.EXE, and that jumper JP4 is plugged into the robot board with the robot power off, and just follow the instructions on the setup page.
 
This may all sound complicated, but it isn't so bad.  You can't really break anything if you screw up any of the steps, but make certain first that you get the v1090 firmware set up on the radios, and let us know how this works out.

Pardon me for jumping in but I had the same problem as you are having with the lpc21isp.exe program, and still do have to catch it at the right time.
 
You wrote:
"When I start lpc21isp and turn on power on the robot as specified, the program just continues synchronizing and then terminates with "no answer on '?'". "
 
My solution:
If I wait till there are more than 5 or 6 dots past the word Synchronizing  (Synchronizing ...........) the program will end just as you said.  I keep my finger on the SRV1 OFF/ON switch and just a couple of seconds after seeing the DOS screen starting to display, I hit the ON switch.  I sometimes have to start it one or two times before I catch it at the right place.  I'm getting better at it all the time.  I try to catch it just as the word Synchronizing starts to print.
 
Robert
 
 

Also, make sure the programing jumper is in the correct position.  I've been there, done that!
 
Robert