What does this pop-up mean, plse?

At one time, MPEGs were a third-party plug-in in Premiere Elements and you needed to activate the plug-in the first time you used that software. That was a decade ago, however, and Adobe has long shut down the activation link. If you are just installing this old piece of software, you will not be able to activate this important component.

Try installing the free trial of the current version of the program. That MIGHT install the MPEG component, and you will then be able to use it with version 11.