UPDATE: Called Adorama. They were nice, but I'm outside the 30-day window for return/exchange. They gave me the Nikon warranty #. Called Nikon, and the guy was helpful. Walked me through a thorough camera and card re-set, but the CardERR message still showed. He approved sending it in for warranty repair and gave me a ticket number. However, as a last ditch attempt, today I exchanged my SanDisk 64GB for a new one and will try that, just in case I got the 1-In-A-Million bad one. Stay tuned.
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I was going to ask earlier but didn't... Have you tried reformatting the SD card in your computer? I don't mean reestablishing the folder system like you do when you reformat the card in-camera, I'm talking about full-blown reformat of the file system using FAT32. This is the only way to correct potentially bad sectors on the SD card. Formatting in-camera is NOT the same thing at all.
These are the steps for doing a true reformat of the SD cards file system.
And, I suppose it needs to be stated: Reformatting the SD card file system will irrevocably wipe-out/delete/erase anything and everything on the card. Everything.
Permanently.
Step 1: Bring up Desktop View
If you are not already in Desktop View, bring up Desktop View by pressing the Windows key + D on your keyboard.
Step 2: Open 'Computer'
Open up the 'Computer' window by pressing Windows key + E on your keyboard.
Step 3: Display right-click options
Your SD card should be displayed in the 'Devices with Removable Storage' section. Right-click on your SD card to bring up the right-click menu options. Select Format.
Step 4: Format the SD card
In the Format window make sure the correct File System is selected. It should be set to
FAT32
Clear the check-box for "Quick Format"; you're going to do a proper of job things
Click Start
The formatting process will take several minutes... Like twenty, so put a kettle on the boil or something while you wait.
Once the formatting is complete, the dialog box will close and you can remove the SD card from your computer.
Step 5: Format the SD card in your camera and...
Voilà! You're done.