I don't get the difference between git rebase origin and git rebase origin/master. In my case I cloned a git repository twice. In the first clone I have to use git rebase origin and in the other clone I must use git rebase origin/master.
An example: http://paste.dennis-boldt.de/2011/05/11/git-rebase
git rebase origin means "rebase from the tracking branch of origin", while git rebase origin/master means "rebase from the branch master of origin"
You must have a tracking branch in ~/Desktop/test, which means that git rebase origin knows which branch of origin to rebase with. If no tracking branch exists (in the case of ~/Desktop/fallstudie), git doesn't know which branch of origin it must take, and fails.
To fix this, you can make the branch track origin/master with:
git branch --set-upstream-to=origin/master
Or, if master isn't the currently checked-out branch:
git branch --set-upstream-to=origin/master master