The Content Package definition is required in the manifest file error

From what little I've found on the net, this is an issue specific to SF.

My course loads and runs fine on ScormCloud, yet when I load the same file onto SF I get the error 'The Content Package definition is required in the manifest file'. I've been through the file and compared it to a known working file and it doesn't seem all that different - a couple of things that when changing didn't make a difference, so I don't think it's anything wrong with the code in the xml file.

So I'm at a loss - is there anyone here that has had this issue and found a solution?