Don't know the fix River, But you can get around it by manually downloading the files and extracting them to you gamedata folder at the moment.Made an account to confirm I'm having the same issue, just cropped up recently. Tried a fresh install of both MBII and JKJA, can only get to StarChild's screenshot after it fails to load and PC gives me the option to "Restore version"
Yeah we had quite a few people asking about this in the AU scene, StarChild included, he was able to manually download and install the files with no Issue.That may not work in this case as the downloaded version is still validated against the online manifest.
The manifest format was changed quite considerably when the halloween map was pushed out. I will revert to the old formatting within the next few hours.