Either you or some software package changed the merit of the MainConcept MPEG2 DirectShow filter. That version of Premiere still relied on DirectX for playback and encoding.
There are several tools available for changing the merit of the DirectShow filters, but their use is not for the faint of heart. GSpot and RadLight Filter manager are the ones I use.
Thanx Jeff for your comments.
It seems that the problem may have been temporary for reasons
I cannot determine but in any event the Main Concept decoder appears to be again working as it should and I have been able to successfully burn my latest DVD production.
I will keep your suggested solution in mind should it again play up.