I'm getting a random messgae on my DS Screen after i've downloaded

When i've downloaded a game and transferred it onto my G6 FLASH the game starts and then it says a message 'the save data could not be accessed, please turn the power off and re insert the ds card' what does this mean?? and why cant i get any games? :-(

https://www.romulation.org/forum/index.php?topic=1462.0
also, if you haven't, get the newest firmware for the card.