Not enough RAM

It has to do with Windows 10 1803 that changed how memory is reported and Adobe products are confused and thing there isn't any.  The only fix is to use RegEdit to add a registry key that tells Elements how much memory your computer has:  4000=4GB, 8000 or 8GB, etc.

Adobe created a help page about what to do that I can't seem to find the Elements version of, it happens to Photoshop as well, but I wrote up something with a few more screenshots that illustrates the same process.  The two things that can be different are the version of elements to add the registry key to.  PSE 2018 is 16.0, and the amount of ram on your computer might be different, the last item of my first paragraph, above:

https://forums.adobe.com/message/10399008#10399289