Yes - Did you at any point get a new xbox via warranty/RROD? Or have you simply changed the xbox at some point? This usually causes this problem.
You will need to delete any Optional Media Updates on the xbox first.
Then create a new silver account, and sign in to live.
Then try and play the file from disc, which will trigger you to re-download the Optional Media Update.
You should then be able to play files from disc without being connected to live.
Simply deleting the Optional Media Update and redownloading it with your normal live account won't work. You must create a new account.
I guess this is DRM or something?