There's a bunch of different things that could be said here and might all be relevant. However, when it comes down to it, any problem of replaying a video DVD mostly falls into one of the following two categories:

1.) readability issues: The player cannot even properly and consistently read the actual data on the disc in the first place - for whatever reason. It could be an older player that generally doesn't like replaying "homemade" DVD-Rs, or it might just not like the particular blanks you're using or cannot read them very well. In this case proceed with standard troubleshooting procedures like trying different makes/types of blanks, avoiding DVD-RWs and burning slow (for best readability). Having up-to-date burn routines for your Magix program (from support website) and firmware for your optical drive is always a good idea.

2.) compatibility issues: The player can read the digital data from the medium but cannot properly process it. This will probably be answered by the player with some kind of more or less straightforward error message. Potential problems here: You didn't actually burn a proper, standard-compliant video DVD, but picked a different output format in Movie Edit Pro that is intended for some other purpose (e.g. replay on the PC), or you accidentally burned in the wrong video standard for your DVD player/TV. Make sure that the program/project settings and MPEG encoder settings (when burning) are set to the proper TV/video standard that applies in your country (PAL or NTSC).

I hope this helps.