There's some links here: CODECs list and alternate players for Movies where you can find an alternative program or a forum for dvd converting issues.
Burn your dvd's at low speeds & make sure they are in the appropriate format (UDF) & not a data disk. Also make sure your set-top player can play dvd-r's including the brand of media you're using. Some are brand sensitive. Experiment with a dvd-rw if your player can play those.