disk error code -81 (r4isdhc)

I'm using a mac, and "the unarchiver" to unzip files.
All nds files I've tried moving on to my r4isdhc and tried to open show this message:
"disk errcode=-81 Please reset system".
Anyone know a solution?

Update your firmware to the latest supported on your card.
Go to the website listed on the box/packaging, or go to www.linfoxdomain.com/ds and select the firmware for your card.

Make sure you have the latest firmware. http://linfoxdomain.com/ds/ Backup all your files and format your MicroSD.

i have the latest frameware and I get this error code 81 , before i updated i was able to play metroid hunters but now get the error code , its making me mad ,anybody know whats going on or how to fix please tell !