It's a good thing that you're finding these things now before you fly it. I assume that your other planes work without problems? Even on rang checks?
It would be a good idea to get someone else to hold the radio, walk away and rang check it and try to work the surfaces while you stand with the airplane and see what it does, if you have not already done so. If it disconnects every time even with different receivers, you're radio might have a connection problem. I had a similar issue with a DX7 and I sent it back and they fixed it free of charge, It's never a bad idea to send the thing in for maintenance every now and then anyway.
If the problem persists, I agree with the others, send the radio in.
Thanks
Brian
rc girl are you using a 821 for your throttle servo ,if so check that,a friend of mine had the same problem and turned out that he was over driving the servo and burned it up ,plus his end points were wrong
if you are using a 821 get rid of it and get another servo
dsm2, dsmx has nothing to do with your problem,also remember you are using a dx6i with a ar7000 rx so you can only use 6 channels,also check and make sure the your 6i is set to US power and not europe power setting,i think its the very last screen on page 2 of the transmitter
Don't just test to see if the surfaces work. Test if they are going in the right direction. Seen this mistake and its usually fatal.