When I try to share for PC playback with MPEG2 using multiplexing I get a "multiplexing failed" message despite trying various settings. If I try to with no multiplexing I get an mpv and mpa tracks but not mpg track with included audio.
How do I get simple mpeg2 as one .mpg file?
You shouldn't be getting a "multiplexing failed" error message. I've never seen that.
There might also be a chance that there is a problem with the source video and audio. What happens if you start a new project and add only the universal counting leader or the bars and tone to the timeline. When you export, does it work?
If that little test fails, then you should do a repair install of Premiere Elements and see if that fixes the problem. If it doesn't fix it, then uninstall Premiere Elements and then do a new installation.