Thank you for your help and guidance. I am using WP Control to monitor the CRON functions.
I did the plugin deactivate/reactivate as you recommended. I now see the PTA CRON function for your plugin on the list of events displayed by WP Control and several reminders were also sent out. Also, the custom roles were restored and all of the signups are still present. Whew!
I will keep an eye on things but I think the problem is resolved.
Again, thank you for your prompt response and a very useful plugin.