Question about dubbing

I have a problem dubbing programs from HDD onto a DVD disk using a Sansui DVR. Dubbing works well for small 30min programs or just after recording to HDD. After a few days trying to dub programs longer than 1hr the DVR shows that it is dubbing but doesn’t finish the process even after hours meaning I have to switch it off and on again of cause damaging the DVD disc.

This could be a problem of size versus quality.
Please be more specific about the setup.