I think the problem is definitely caused by the space in your user folder. A fix for this issue(ATLEDGE-464 SketchUpload recognizes Windows paths with spaces by bbaltz505 · Pull Request #20 · intel/intel-arduino-tools · GitHub) has already been submitted to the appropriate repository but has not yet been merged. You can manually make the changes to your C:\Users\Beat Arnet\AppData\Local\Arduino15\packages\Intel\tools\sketchUploader\1.6.4+1.14/clupload/cluploadArduino101_win.sh as shown here: ATLEDGE-464 SketchUpload recognizes Windows paths with spaces · bbaltz505/intel-arduino-tools@bd207be · GitHub
EDIT: the pull request fixing this issue was merged 2016-01-05. This issue should be fixed if you are using the latest version of Intel Curie Boards.