What is your workflow? If I go to Composition>Add to Media Encoder Render Queue, it adds it to the Media Encoder render queue just fine.
What happens when you do that?
It opens media encoder without the file. when I try to add manually I get an error message.
I am currently doing a clean install. Adobe obviously doesn't have respect for the time of the people that pay for their products.
Hopefully your clean install fixes it.
If it doesn't work and you want help, please respect our time and give us more information so we can help you. We would need to know things like what that error message said, for example.