I also have the same problem.
I installed Wavelab LE, than I bought mp3 upgrade patch and installed it. I also tought that it was successful. It wasn’t.
In my File Format -> Factory presets in Render mode I only have 3 kinds of wave, and few encoded ones (FLAC, Ogg and WMA), none of them is MPEG. I also don’t have MPEG in types of file format when I click ‘edit’ in presets window.
What could go wrong?