I think others have reported similar problems, and you might be able to find solutions if you search the forums. (Never happened to me, so I don't remember what the solution was.)
Remember that you have at least two other options for updating your data, though; I bet if you get past this bump, future updates via wi-fi will start working again.
Option 1: Use a USB thumbdrive, and visit the "Updates" page on the AP site to download your update data, then transfer the USB drive to your 720 for installation: http://ifly.adventurepilot.com/UPDATE...
Option 2: The fastest way to get a big update installed requires an SD Card read/writer and a Windows PC. If you have those two things, install the iFly Connect software from here ( http://ifly.adventurepilot.com/UPDATE... ), then pop out the SD card from your iFly, insert it into your computer's card reader, run the iFly Connect tool, then replace the SD card back in the iFly.