Application Error Question - Error Message... <SUBSCRIPT>buildRuntimePathFromIndex+135^EnsLib.EDI.X12.Document...

An X12 / 271 message shows "Completed" on the BO. However, it did not reach its destination. I searched for more information on what the error means but, couldn't find much. See error enclosed below. Any idea what it means and how to fix it?

More info...

• The IOLog Record shows in the Output Data an error... "An error occurred with the web application. It has been logged to system error log (System Operation > System Logs > Application Error Log)."
• The EDI response shows the same message... "An error occurred with the web application...." 
• I re-sent the message from the BO and it went out successfully and reached its destination. 

Error logged in the Application Error Log: