3DS / R4i Help

Hey folks looking for some help if possible.

I put games & videos on an R4i card about a year or so ago for a friend's kid.

Recently the card became blocked and when you try to access it the following message is displayed:
An error has occured.
Press and hold the power button to turn the systen off.
Please refer to the Operations Manual for details.

The 3DS itself is running Ver. 5.1.0-4E, and the wireless access is turned off and blocked by parental PIN, so I don't think the kid managed to update the DS, this can block cards right ??

I reformatted the card and loaded the latest available R4 software I could find; R4i-3DS V1.80b, but the card remains blocked and still displays the above error message.

The thing that has me stumped is that the card plays fine in the DSi consoles that my own kids have.

Thanks in advance for anyone taking the time to read & for any advice..............