You're in the 3DS eShop for the first time, and it offers to link your Club Nintendo account to your 3DS, presumably to help you rack up stars and benefits. You judiciously input your email address and password, only to have an error message appear, telling you that your email address and/or password is incorrect. So you hop on your computer and login to the Club Nintendo website without issue...
According to the Troubleshooting section of Nintendo's website, this error can be caused by two things, neither of which are mentioned in the original error message, and neither of which has anything to do with an incorrect email address or password.
Here it is:
- Login to your Club Nintendo account via the relevant Nintendo website (on your PC, laptop, phone - basically anything other than your 3DS!).
- Click on the "EDIT MY PERSONAL DATA" button.
- Under the "User Data" section, click on the little "EDIT >" button.
- Click into the "Username:" field and remove any "special characters" from your username. This includes underscores ("_"), and I assume other symbols used for swearing like !@#$%^&*()-+=, etc. If you've always hated your username, here's your opportunity to change it.
- Check the "Date of birth:" to ensure that you are registered as being born more than 13 years ago.
That being the case, I would recommend trying to contact Nintendo customer service to see if they can change it on their end (which is probably more time consuming than it's worth), or failing that, give up and create a new Club Nintendo account. A date of birth greater than 21 should have you covered, but you might want to make yourself 100 years old just to be on the safe side...
I wrote this because I found Nintendo's troubleshooting instructions to be woefully low on detail and generally unhelpful. I am a trainer by day, so I thought I would try writing some instructions that were quite the opposite!