Oh God, I now know the problem. I analysed the Data with 2 Computers, half on a Windows computer (C:\Program Files\BrainSuite17a\svreg\BrainSuiteAtlas1\) and half with a MacOs Computer (so the path is not the same).
Is there a solution for this? Do I need the svreg. files for all of the patients and edit the path every time or is it just for the first case? Because in the ICBM25 folder that I downloaded from the Brainsuite page was only on the first patient present.