R4i troubles

This morning, I turned on my DSi and started up my R4i cartridge. I received this message."System date error! Please check NDS system date."It's been working absolutely fine for 6 months until now. I hadn't changed any settings on the DSi, so I don't know what's caused this. I thought it might want me to change the date on the system, but that did nothing. After that, I checked the contents of my micro-SD card & there was nothing wrong on there. As I said, it worked as normal yesterday and I haven't added any new Roms onto the card or anything like that. This just sort of came out of nowhere.Any advice?

set the DS date back 10 years or something like that

I think its to do with the auto boot on R4is try turning the date back. May work