How weird, that didn't happen to me. I just checked and I can continue my save just fine. You told me that your R4 was new so maybe you are using an old version of the kernel so go to the R4 site and get the latest one (v1.18 is the most recent, it's several months old but the game works fine for me). Don't ask me how to apply the new kernel because there are instructions in the site and it is easy enough to do.
I don't have an R4, it's DSTT and diamond works just fine so i don't think the problem is the kernel unless i'm missing something... Also i get the black screen after i select continue on the emulator, not on the DSTT, that one can't even load it (i tested platinum on the emulator first and then tried playing it on the DSTT). But anyways, thanks for the help