If some pages of the plugin are not loading correctly you may want to turn on WP Debug mode temporarily to see what’s causing the error.

A few know issues are:

Fatal error: Uncaught Error: Call to undefined function bcpow()

bcpow() is a default PHP function so if this function is undefined it means it’s not configured on your server. Most likely BC Math will be missing in the PHP configuration. You should contact your hosting provider or server admin to get this function up and running.