HTTP ERROR 500

I converted my site from V1 to V2 two days ago, and I was able to make page changes using two different Themes. I started with Astra and ended with Supreme Directory.
I logged in yesterday and was able to make page changes using only Supreme Directory as the theme.
Today when I tried to log in to the WP Admin area, the following message popped up:
This page isn’t working
*************.com is currently unable to handle this request.
HTTP ERROR 500

This is the same error I received when I first tried to convert from V1 to V2 using the old conversion instructions (i.e., move the GeoDirectory plugins to a backup folder). The conversion was successful after using the new conversion instructions.

If I just type the non-admin name in Chrome, the “Coming Soon” page opens as it should.
What do I need to do to be able to log in to the wp admin area again?