Ok, everyone. I was able to solve my problem with the information on this page.
https://contactform7.com/2016/01/15/red-border-error-issue-on-wordpress-441/
In my particular case, the From email address I had been using, and which had worked in the past, no longer represented a valid configuration for From email address. It had been a wordpress email address using my domain name. I instead changed it to an email address on my host server, which also has my domain name and the problem was resolved.