Here is a DVD Studio Pro tutorial that will outline why media may have become disconnected in your project and how to repair the problem.
Disconnected media can be just as much of a problem in DVD Studio Pro as it can be in Final Cut Pro. Disconnected media occurs when DVD Studio Pro cannot find the media that it has listed on its Assets directory. The Assets are all the media that are being put onto the disc, from the video and audio pieces that are being placed onto the tracks to the music that is being used in the menu. If that media is moved at all, or deleted for whatever reason, then you are going to find that it becomes disconnected. Relinking media in DVD Studio Pro is actually a relatively easy process.
Setting the Relink
You have a couple of options of when to relink the media in your DVD Studio Pro project. When you first open up your DVD Studio Pro project you will likely be notified if you have missing media. There will be a list of the media that DVD Studio Pro cannot find and you can either continue past this without relinking that media or you can select one of the disconnected pieces and select to find it. You will then browse through your storage drives to find the missing piece of media, selecting it once you do. If there are other pieces of disconnected media near to where you found the first piece DVD Studio Pro will tell you that it is relinking those as well. Once this is done then all the media will be relinked.
If you are already working in your DVD Studio Pro project and notice that some have your Assets have become disconnected, which will be indicated by their text turning red or problems in locating them when trying to play them in tracks, then you can do it there as well. You will simply right or control click the assets in question, choose to Relink it, and then go through the same process as before.
Preventing the Disconnect
Preventing the disconnect of media in DVD Studio Pro is a little different than in Final Cut Pro as you are not managing large amounts of media for a long editing process. Instead you have to export them from Final Cut Pro, compress them in Compressor, and then import them into DVD Studio Pro. This essentially means that if you accidentally lose them you can actually just recompress them and then import them back into DVD Studio Project, effectively solving the disconnect problem. The best way to avoid this is to take all the assets that you are using in one DVD Studio Pro project and place them in one folder. If you move that folder make sure to relink all the media right away so as to avoid this problem when you are trying to finish up your DVD authoring.