Error Message when opening sent translation projects

Hello, Team!

I'm working on the translation end of Trados and cannot open one of the translation packages I was sent. In the Open Project window, an error message reads "The specified folder already contains files. Choose a new or empty folder." (translated, got the message in German). I'm shown that there are files in the project, but the project simply won't open, as the "Finish" button isn't active. Has anyone else encountered this problem? I would be very thankful for your help!