It's not about uninstalling Corona, it's about removing any Corona related content from your scene, that's what the error is about. Max complains about Corona content which can't be properly opened without Corona installed.
You need to remove any Corona related content, there are various places where to look:
- what's the current main renderer? If it's Corona, change to something else
- Convert materials/maps to something else
- keep in mind that the UVUnwrap modifier may still refer to Corona specific maps. To reset this, select each object with an Unwrap modifier that had a material with a Corona map assigned, open the UV Editor and reset maps in the top right roll down menu. Repeat for every object with materials that have used Corona maps
- Delete Corona Lights
- Delete or convert any other entity specific to Corona (Proxies, Portals etc.)
I may have forgotten something.