I had this problem on my R4 a couple of weeks ago - it seemed to happen when I removed the card from my PC without properly ejecting it.
What I did was copy, one by one, the SAV files off the R4DS then deleted them off the R4, and restarted my DS until the R4 card worked again. I then knew which .SAV file was causing me trouble.
I then deleted the new .SAV file off the R4, copied back the original .SAV file and lo and behold it all worked fine!! The problem game for me was Professor Layton, but it could be just fluke and that any game could have cause this problem.
Frozen R4
I had this problem on my R4 a couple of weeks ago - it seemed to happen when I removed the card from my PC without properly ejecting it.
What I did was copy, one by one, the SAV files off the R4DS then deleted them off the R4, and restarted my DS until the R4 card worked again. I then knew which .SAV file was causing me trouble.
I then deleted the new .SAV file off the R4, copied back the original .SAV file and lo and behold it all worked fine!! The problem game for me was Professor Layton, but it could be just fluke and that any game could have cause this problem.