I've spent about 3 hours working on my New 3ds trying to get my content transfered from my launch 3ds. The issue I'm having occurs at the end of the SD card transfer. I select the second option to move save data and redownload games and such on my new system. The process starts and gets to the very end (past 75%, one or two pieces away from completion) and then fails. The old system tells me that it cannot detect an SD card.
"An error has occured. Could not detect an SD Card. Please reinsert the SD Card or insert a different SD Card and then try again."
On the new system:
"An error has occured. A local wireless error has occurred. Cancelling transfer. Please try again."