I received these errors on an Exchange Server running Windows Server 2003 and Exchange Server Std. 2003 SP1 with Symantec Mail Security 126.96.36.199. After receiving many EventID 45 errors from Symantec Mail Security, Exchange became unresponsive and logged many EventID 348 from source MSExchangeTransport errors until we rebooted.
After the reboot, contacts in a public folder could not be opened, or had a message about Symantec replacing the message body in the notes field in the contact. The message body was quarantined (per my SMS configuration). I released many of the quarantined messages files, which were empty .rtf files.
I contacted Symantec TS and the tech stated that version 4.61 fixes several known issues including memory leaks, and problems scanning contact folders and calendars. Symantec would not provide any technical articles or release notes regarding the issue and I could locate nothing in their knowledge base.