Error -2125

Try Share/to Media Browser. Then drag into iDVD from the Media Browser in iDVD.

I have never seen an official list, but I think it means you are out of memory, which could happen with a long video. How long is your video?

Yes. That is the problem.
iMovie is meant for home video, and your video is longer than 90% of the feature films out there.
For feature length films, I would recommend a pro video editing app like Final Cut Pro or Final Cut Express. These apps can "render as you go". You can render a sequence or a nest of sequences so you don't have to do it all at once. iMovie renders everything in one pass when you use the Share menu.

11MB is not enough space on your disk. You need more space to allow room for OSX to manage virtual memory. You don't mention which Mac you have, but I would consider moving some files to an external drive to free up space on your internal drive. I would want 30 to 40GB free when I was starting a big render like yours. It is possible that if you had more space, your project would render, but iMovie is really not the right tool for a movie this long.

(Note: if you are moving iMovie files to an external drive, be sure to read up on how to do this within iMovie so you do not mess up your projects.