Today I installed beta 16 on a SanDisk Extreme 16GB, copied all my roms and save states from the old card and now everything works fine.

Nils, what is the brand/model of your sd-card? For me it also works with some games, with others it doesn't. I played Zelda for at least 2 weeks without any problems, now it doesn't load/save anymore, but I also played Harvest Moon (both SNES), which still works fine. I also have problems to copy files over to share/roms/ from time to time. I didn't give much about it cause the other day all copying works fine again, but those are exactly the problems people get with "cheaper" sd-cards. As I know now my SanDisk Ultra series and also some Transcend seem to make problems.

Ok, I'm almost sure it has to do with my "cheap" sd-card. I use a SanDisk Ultra and many people seem to have problems with it after a few days. I sshed into the box and noticed that with every reboot the sd-card is mounted randomly as read/write or read only. Though the save states also won't load when mounted rw I'm sure it has to do something with reading/writing to the card in general. I ordered a Sandisk Extreme now, hope the problems will be gone then.

It's beta 14 for me. I remapped the Xbox Controller but it didn't get any better. Now I updated to beta 16 but still the same (also remapped controller).

I have exactly the same problem in the Super Nintendo emu for a few days now. I played Zelda 3 very frequently over the last 2 weeks saving and loading states a lot and suddenly I get the same error Nils. Save and load don't work anymore in the game, what can it be?