I've been having this issue with some Xbox 360 downloadable content and it's really bugging me. I've yet to call the unhelpful Xbox support, though I did sent the support an email several months ago (never got a response, btw.)
It seems that with some of the downloadable content I have on my 360, I can only access it when I'm connected to Xbox Live. Problem is, I'm not always connected to Xbox Live. For me it depends on which of my roommates my hard drive is on, whether or not I need the internet connection on my laptop, etc.
This seems, um, wrong. It happens even with paid content. For example, it would not recognize my Shivering Isles expansion on Oblivion unless I was actually signed in to Xbox Live, nevermind the fact that Shivering Isles has nothing to do with being online. It has also happened in both Guitar Hero II and III. But it doesn't always happen, and it's not with everything. Last time I played GHIII I had the most recent stuff showing up but not the earlier songs. WTF?
Has anyone else had this problem or heard of something similar? At least I can know I'm not alone. I doubt anyone knows how to fix it but that would be appreciated too if you know.
And, to clarify, this was happening before Xbox Live imploded.