Not possible to submit .pdf files as version through Shotgrid Create

Hi Shotgrid
I’m a storyboard Supervisor trying to use Shotgrid to review Storyboards: The Storyboards are delivered in PDF files. But if I try to upload a new version through Shotgrid Create- Create displays a error message that “We has trouble loading the media” Am I doing something wrong, or is it a bug, or is it simply not possible to upload PDF files as neww versions through Shotgrid Create?
Best Mads