When releasing a message from Spam Quarantine or submitting a message as missed spam you receive the following response from the Messaging Gateway Control Center:
Cannot submit the selected message(s) to Symantec Security Response. The request cannot be processed because request exceeds the limit size. For more information, see the Help or product documentation
The internet web API which processes missed spam or false positive submissions has an upper limit on total message size which has been exceeded by the submitted message.
This is expected behavior for missed spam or false positive messages that exceed 5 MB.