There are several reasons an image or file may not upload to Cascade. First is if the file size is larger than the 10 MB max allowed by Cascade Server. Typically you will get an error message if this is the issue.
The second reason could be because of the the file name of the file that is being uploaded. If the file contains any special characters such as parenthesis or percentage signs the system won't except the file. This issue however does not throw an error so it is a little more difficult to notice.
Another reason could be the file type is not supported. Cascade excepts most file types (pdf, doc, xsl, ppt, jpg, gif, png, etc.)