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Okay, I'm really stuck here. I got a 7 digit answer and it's plain text, except the last character. But it doesn't seem to be correct, where could be my mistake? Obviously there's a solution, why is my last digit not alphanumeric?

Hello everybody, I'm stuck at the beginning. I realized what the image wants to tell me and I used this information to create a new file. It looks perfectly when peering into the depths, header is okay and I think I can tell what kind of file it is and what is's supposed to do when accessed. But the...