@John-Hunt

Welcome to the Magix user to user forums.

First, please DO NOT POST ALL IN CAPITALS! It is considered to be the forum equivalent of SHOUTING and may cause other users to ignore your post.

Unfortunately, you have given us minimal information to be able to help you. Please read this post and give us ALL the information requested there. Then please tell us the exact variant and version that you upgraded from and to. Then please tell us which mp4 codec you are trying/needing to activate. The default codec is normally more than sufficient for most mp4 videos, so please also find, download and install the free MediaInfo utility, point it to one of your videos which no longer play in MEP and post the results of the Text view here.

Jeff
Forum Moderator