Update 07.10.2016: The problem is fixed and the One Drive integration with Assignment is working again.
We are currently experience a problem with the One Drive integration with Assignment.
After clicking on 'Upload from One Drive' button, the window for uploading appears in the right hand corner. But it will stay in a forever loading state.
Workaround: Please use the other upload option. If you want to upload a file that you have stored in your One Drive, please first download it to your PC and then upload it from there to the Assignment.
Our developers are already working on this issue.
We will update this article as soon as the issue is fixed.