Welcome to the Magix user to user forums, so not a contact for any Magix staff.
Because of this, unless you give us a lot more information it is highly unlikely anyone who posts here can help you!
Start by reading this post and give us ALL the information requested there, along with details of the exact version, variant and build of MEP which you have (check under Help>About). Also, tell us the exact wording of any error message you see. As a matter of interest, why do you want to be able to use the, now rather old, Main Concept codec?
Please do not hijack another user's thread by posting a question which has nothing to do with the question raised by @Petar-Petrov.
Please create a new thread with your question, giving full details of your computer, the exact version and variant of MEP which you have and as much precise detail as you can about exactly what you are trying to do.
The button at the top right when you are not in a thread says "New Post." When you are in a thread, it says "New Comment" which is the same as going to the bottom of a thread and adding a comment - on the thread.
As Jeff says, start a new post and include sufficient detail as per the instructions that you'll see when you create a post so that we don't have to play 20 questions.
Give the post a good title, representative of your problem, so that others who have a similar problem can find it easily.
I think that most of us in the forum have written off Main Concept as it created problems for some users. I don't even bother to install it anymore. Maybe Jeff can comment more on this.