We've located a bug with this message and fixed it in the 1.06 kernel, I'm sure we'll be able to release the new kernel soon, until then please don't run "Casper's Scare School Spooky Sports Day! ". In the meantime we are working on a recovery...
Sorry to hear you're having this issue.
The fault you describe looks like the card can't detect the insertion of the SD card properly, can you check if the metal contact points of your SD card are oxidized or dirty, also please check if all the...
Your microSD card have corrupted cluster, you have to backup up your save immediately. and use any disk scan software to fix your microSD card, which the Windows system have a disk scan tool can do it.