For a student project, I had to make an arducopter, all is fine ... without the Xbee modules.
In fact, I can't get them comunicate in the two ways. I succeeded to receive something from the APM board but I can't transmit something to it, so when I try to connect using Mission Planner, It says "Getting params[...]" and then in the console I can read "Lost xxx pkts xxx" and, after a while it says "Read timeout[...]".
I tried the test code and I can get the "port 3" message so the communication on this way is working fine.
I have two Xbee Serie 2 rev.F modules, A xtreambee FTDI adapter and another USB adapter for the computer.
I checked the connections between the FTDI adapter and the APM, all is ok.
As some people said, I solded the CTS and the VIN pins.