For anyone else with this problem or future googlers, here are the steps cribbed from [Truth] to fix this error on Wii U vWii when using configurable USB Loader (cfg USB Loader) to load Wii backups or ISOs from an SD card or SDHC card:


Note: DO NOT install any Wii cIOS on Wii U vWii.

Lets go:
Download the following package:
www.mediafire.com/?n2zl8v5kn288j9d

1.) Extract the contents of vWii_cIOS_apps_20131218.zip to the root folder of your SD card.
Note: Make sure that you don't have any original Wii system files (like wads) on your SD Card!

2.) Launch d2x cIOS installer from the Homebrew Channel.

3.) Select cIOS : <d2x-v10-beta52-vWii> not d2x-v10-beta53-alt-vWii.
Select cIOS base : <56>
Select cIOS slot : <249>

4.) Press A to install and wait for installation to finish.

5.) Press A to continue.

6.) Select cIOS : <d2x-v10-beta52-vWii> not d2x-v10-beta53-alt-vWii.
Select cIOS base : <57>
Select cIOS slot : <250>

7.) Press A to install and wait for installation to finish.

8.) Press A to continue.

9.) Select cIOS : <d2x-v10-beta52-vWii> not d2x-v10-beta53-alt-vWii.
Select cIOS base : <58>
Select cIOS slot : <251>

10.) Press A to install and wait for installation to finish.

11.) Press B to Exit.

12.) Launch newest CFG USB Loader MOD from the Homebrew Channel.
Note: To copy game images from PC to your SDHC card with the correct folder names and structure, use Wii Backup Manager.