Fatal Error after upgrading to 4.7.13 from 4.7.11

Question

Just upgraded Civi from 4.7.11 to 4.7.13

The upgraded installed successfully, but rendered Civi functionally unusuable. Attempting to click on any tab within Civi (such as navigating to Contributions, Mailing, Memberships, etc.) results in the following fatal error in the web browser.

Any assistance is appreciated! Thank you!

Fatal error: require_once(): Failed opening required 'CRM/Core/Payment/EPayUCM.php' 
(include_path='/home/WEBSITE/public_html/drupal/sites/all/modules/civicrm/drupal/modules/civicrm_engage/:
/home/WEBSITE/public_html/drupal/sites/default/files/civicrm/extensions/uk.co.vedaconsulting.gotowebinar/:
/home/WEBSITE/public_html/drupal/sites/default/files/civicrm/extensions/org.civicrm.module.cividiscount-2.5/:
/home/WEBSITE/public_html/drupal/sites/default/files/civicrm/extensions/civicrm_stripe-4.5-dev/packages/:
/home/WEBSITE/public_html/drupal/sites/default/files/civicrm/extensions/civicrm_stripe-4.5-dev/:
.:
/home/WEBSITE/public_html/drupal/sites/all/modules/civicrm:
/home/WEBSITE/public_html/drupal/sites/all/modules/civicrm/packages:
.:
/home/WEBSITE/public_html/drupal/sites/all/modules/civicrm:
/home/WEBSITE/public_html/drupal/sites/all/modules/civicrm/packages:
/home/WEBSITE/public_html/drupal/sites/all/modules/civicrm/vendor/tecnickcom:
/home/WEBSITE/public_html/drupal/sites/all/modules/civicrm/vendor/phpseclib/phpseclib/
 in /home/WEBSITE/public_html/drupal/sites/all/modules/civicrm/Civi/Payment/System.php on line 59

Answer 1

This error is saying, "Hi, there's a missing payment processor file." The payment processor file in question isn't part of core CiviCRM; it's probably provided by a plugin. Is this site associated with UC Merced? It seems like maybe there's a custom payment processor plugin written for their e-pay system.

Since this broke on an upgrade, I wonder if it wasn't a plugin, but they inserted the file directly into core CiviCRM? It's hard to troubleshoot without seeing it. For now, check Administer menu > System Settings > Payment Processors and disable your payment processor to see if that gets your system working. Then track down whomever wrote this custom code for you.