It seems like there may be a few things happening here.
First, this is a "Games for Gold" offer, therefore you must be a Gold member to benefit from the offer. So even if we were to get your permission settings correct, you would be unable to download it for free.
As for the error message, are you seeing that same parental error message for everything you try and purchase/download? If you could provide a screenshot of that message, that would also help.
Let us know, and we can go from there.