Sonic Adventure 2 Battle saving problem

[Korados]

Hello everybody,

I have a strange saving problem again. Recently, I started to play Sonic Adventure 2 Battle again and went through the Hero Storyline.
When I was finished, I closed Dolphin. But after I opened it again, the game said that the save file is corrupt and has to be deleted!
So I tried playing the Hero Storyline a second time. But when I was finished again, the same thing happened!

What can I do about this? I used Dolphin 4.0-8700 and I always keep it on default settings. The only thing I changed was
that I used Single Core Mode because of the graphical bugs.

I hope you can help me with this.

Thank you very much for your help!