System date error

Strange occurance, I've been playing my ds perfectly fine for years, running a standard r4 card. However, I powered it up this morning, to recieve a red message on the loading screen, which reads: ''System date error! Please check NDS system date.''I've checked the date, its all right, including the time. Could anyone shed some light on this situation please? Any and all help is welcome.

You can set the date back to 2000 or something and it works again
or you can download the new firmware from wood v1.06 from here http://gbatemp.net