red giant is unlicensed

Are you using the Maxon app with your Red Giant plugins?  If so, log out of the Maxon app.  Quit and save any open projects/documents.  Restart.  Launch the Maxon app and log back in.  Then open After Effects and Media Encoder again. 

Also, double-check that the version number of After Effects matches the version number of Media Encoder.  So, if using After Effects 24.5 then make sure the Composition is being exported with Media Encoder 24.5.

If none of that works, I'd start a support ticket with Maxon.

A workaround is to use the After Effects Render Queue with the Output Module set to High Quality (or custom ProRes 422 HQ) and then add the resulting movie file to Media Encoder.