Go to your keynote file,click on 'file' at top left hand corner.Click on export.Click PDF or Images.Then try again with the new file.
Thanks Timothy, but then it won't be a powerpoint leh. Is there another way?
Go to google chrome and try attaching your file in there. Safari got some problem
If you just need the link you can download it onto google drive on google chrome then you can get the URL when you finish downloading.