Exchange and Symantec Mail Security

[WCharlier]

I have a uniqe problem. We just migrated out Exchange 2000 to Exchange 2003. We installed Symantec anti-virus 9.03 and SMS 4.6. The problem: Some messages, with no apparant pattern, cannot be read. The problem messages are both pre-existing (having been migrated) and new since the migration, and we can find no pattern (sender, attachments, embedded graphics, html vs rich text...). When you try to open them, you get an "Unknown Error" message. We tried backing down to the older versions of the software that we had had installed on the old Exchange 2000 server, but to no avail. If the service for SMS is stopped, the message sbecome readable. But when you turn it back on, once again you get the errors. If you export the messages to a .PST file, they can be read from the PST, but if copied back into the inbox, they are once again unreadable. If you stop the service, and forward the message back to yourself, then restart the service, the forwarded message is readable, but the original still isn't.