Problem is caused because the class is located in a package and the standard rft boot line doesn't address this circumstance.
I solved it by writing the correct class path in the "path" lines and also writing the packagename before the class (like you would start the program with the CMD line).
RFT Application Wizard:
Path: C:\YourPath\bin
(Eclipse Class folder)
Class- Or Jar: package.packageTwo.KlassName