I received an email recently from a client that was getting this error, "Not a valid SCORM 2004 course" when importing a SCORM course into their Meridian LMS.
He believed that this was a mistake and imported his content into SCORM Cloud and although he received no errors, he did get these parser warnings.
Parser Warnings 
The Sequencing Control Mode 'Control Choice' was detected on a leaf node, but is only applicable to cluster nodes. (Item 'ITEM01')
The Sequencing Control Mode 'Flow' was detected on a leaf node, but is only applicable to cluster nodes. (Item 'ITEM01')
Even with the parser warnings, the course launched fine.
Here was the problem: The Meridian LMS likes packages zipped at the root level, not the outer folder level. Our client zipped the whole Windows folder instead of zipping its contents and the parser warnings went away.