If your content package is contained in a folder structure:
Then select the "Choose" button on the file chooser.
TinyLMS closes the file chooser and verifies the content package.
A message panel is shown when the file has warnings or errors.
If a warning is shown, you may still create a course from the content package.
TinyLMS will show you the cause of the problem on the tab labeled "IMS Manifest".
If the content package has no errors, the controls of the window are now enabled.