I assume you're using wi-fi on a 720, correct?
If so, of course it shouldn't do that, and hopefully someone smarter than me will be along shortly to help you correct that.
In the meantime, there are multiple ways to update an iFly, and you could try a different method.
If you have a Windows PC and an SD card read/writer, then the easiest way is to use the iFly Connect software. Instructions and software are here: http://ifly.adventurepilot.com/UPDATE...
If you can't use iFly Connect, then the other way to perform the update is to use a USB thumbdrive. Go here and follow the instructions on the left side of the page: http://ifly.adventurepilot.com/UPDATE...
Hope that helps.