You may have used illegal characters in the E-Form that have been saved into the database record. When you try to retrieve it, the database thinks the record is invalid. The error message is usually:
"The server provided an invalid response null”.
Or there might be an error in the CDM Coordinator email address. When this happens the error message is:
“The existing notification was not found in our database. Please check your serial number and email address with your email acknowledgement.”