Permission problem by upload files on Windows Server 2012 R2 and IIS

I'm using Drupal 7.31, CKEditor 4.4.4 and the latest CKFinder version. Drupal is installed on Windows Server 2012 R2. The problem: I can upload, download and delete files in the ckfinder folders. All files are visible in the upload tab but not visible in the CKEditor priview window. The NTFS permission is set to the folder and normaly the permission to the file are 'inheritence'. Now when I upload a file to the server, the user folder was created and all permissions was set. Then I upload the file, the file was uploadet in '_thumbs' and then ckfinder create a copy in the folder 'images'. This new created file has only permissions for IUSR, Administrators, and System. Inheritance is not working and no user has access over a browser to the image. When I replace all permission with the folder permission it works fine. I need access for the group IIS-Users and the Network Serverice.Any ideas for help?