There are several reasons why an episode cannot be published.
First make sure that the media plays in QuickTime or iTunes. If it does then the issue is usually related to the metadata of the media.
Log in, click Media Library
in the Publish drop down menu and check the duration of the file. If it is 0:00 then the file will not publish because the system thinks the file has no length. We run a program to correct this every hour so if you wait the file should be fixed.
If none of these fixes work then the next step is to open a ticket here and a support representative will look into your issue for you: Pro Support