In certain cases, PowerPoint 2007 and later will embed content such as charts and graphs as links to Excel rather than raw images. This type of content cannot be handled by our slide conversion system, and thus the upload process will fail. To remedy this, try saving the slide deck as a Office 2003 PPT file rather than PPTX. The PPT format does not support these links, and thus the upload should proceed as usual. You can also save the slides as images and then import the images into another PowerPoint file.
You should also ensure that your slides are not password protected and that the auto-advance feature is turned off.