Welcome to the forums.
Looks like that error message does refer to encoding (see http://support.apple.com/kb/HT1645) but a problem could be that your video has to be reloaded into iDVD if you started the encoding process and then switched settings. You could start a new iDVD project, or try deleting encoded assets.
Let's start from the beginning -- what length of video are you trying to fit on the DVD? (this will indicate what encoding options you have). Double layer DVDs can be finicky and are used for video more than 2 hrs long.
Use good quality media -- Verbatim is often recommended around here, and I've used Sony DVD-R with good results.
For a detailed treatise, see: https://discussions.apple.com/thread/3926901?tstart=0