(SheepSaver error) Sorry, the desktop folder on the startup disk could not be created. Try unlocking the disk
Solution 1:
I had a look at the SheepSaver Wrapper page you're using and think they've essentially been too clever by half. I followed it a few times and ran into various problems I then had to resolve myself.
If I was you, I would stick to the setup at emaculation instead.
However, if you're going through all this effort to try and play Swoop (as per your other question) I suggest it's just not worth the effort. Just my two cents worth.