"Customer Creation Failed"

Also, when I try and edit, I get “The customer update failed, or no changes were made.”

Help please.

Sounds like you may need to re-install the plugin. Delete the plugin, then follow these installation instructions: https://howtononprofit.wordpress.com/classdex/installation/

Hope that does the trick!

If I delete the plugin, will all of my current customer information disappear?
Thank you.

So customer creation was working, and then stopped working?

Your existing data will probably not be deleted, but to be safe you can export all of your tables with the Import/Export function: https://howtononprofit.wordpress.com/classdex/admin-functions/