Fatal Error after upgrading to 4.7.13 from 4.7.11
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.