Cron job crashed due to class 'Plugin' not found

[maxramirez84]

Describe the bug The EM does not send the email notifications and cron job crashes:

The REDCap cron job named "1-minute_notifications" crashed unexpectedly on the server!

Error message: Uncaught Error: Class 'Plugin' not found in /var/www/html/redcap/modules/email_notifications_v1.0.0/EmailNotificationsExternalModule.php:341 
Stack trace: 
#0
/var/www/html/redcap/modules/email_notifications_v1.0.0/EmailNotificationsExternalModule.php(448): ISGlobal\EmailNotificationsExternalModule\EmailNotificationsExternalModule->notify('minute') 
#1 
/var/www/html/redcap/redcap_v9.0.0/ExternalModules/classes/ExternalModules.php(3335): ISGlobal\EmailNotificationsExternalModule\EmailNotificationsExternalModule->minuteNotifications(Array) 
#2 
/var/www/html/redcap/redcap_v9.0.0/Classes/Cron.php(295): ExternalModules\ExternalModules::callCronMethod('1', 'minute_notifica...') 
#3 
/var/www/html/redcap/redcap_v9.0.0/cron.php(22): Cron->execute() 
#4 
/var/www/html/redcap/cron.php(11): include('/var/www/html/r...') 
#5 
{main} thrown 

File: /var/www/html/redcap/modules/email_notifications_v1.0.0/EmailNotificationsExternalModule.php 
Line: 341

To Reproduce Steps to reproduce the behavior:

1. Enable the EM at any project
2. Configure the EM to send notifications to some user
3. Send one or more records from REDCap Mobile App to the project
4. Wait and the [REDCap] Cron job crashed! email will be sent to the Administrator.

Expected behavior Send the notification in the specified interval without receiving any error email.

Screenshots NA

Desktop (please complete the following information):

• OS: Ubuntu 16.04.3 LTS
• Browser: Chrome 65.0.3325.181 (Build oficial) (64 bits)

Smartphone (please complete the following information): NA

Additional context NA