Sending e-mail with new comment failed: SendEmail failed. First exception on row 0; first error: UNVERIFIED_SENDER_ADDRESS, Organization-Wide Email Address has not be verified for use.: 
Check Setup > Email Administration > Organization-Wide Addresses and verify that each address you are using with E2CP is verified.
This is due to a Salesforce configuration issue.
See Salesforce Help & Training for more information about Organization-Wide Addresses.