I was travelling with my new 3DS XL in sleep mode (screen closed, game still on). When I arrived at my destination, I opened the lid to continue my game but an error message popped up onto the screen stating the system encountered an error and needs to be turned off and turned back on. The only way to turn it off was to hold down the power button for a few seconds. When I turned it back on and tried downloading something from the Nintendo store, it stated my NNID had to be linked to my 3DS. I had already linked my NNID when I purchased the new XL back in February (and had no problems before the forced shutdown). When I went through the process this time trying to use my existing ID, it states my ID is already linked with another member of the 3DS family...which is the one I hold in my hands and is trying to say that it isn't!... All my info on the 3DS system appears correct, including my purchase history in the Nintendo store but my NNID is no longer linked and won't allow me to use my already existing one (which is also linked to my Wii U and the Nintendo site).
How do I fix this and re-link my NNID to my 3DS XL?