If you can determine what the source interface is, let us know if the source interface of the message in the error DB is an outbound interface.
If that is the case, probably something with replies being treated as data with no route defined.
A reply with an extra new-line character erroneously added for visual effect happened to me once resulting in a reply and then a confused interface that had an extra new-line character or a empty message as you might describe.
If the errors are on an interface listener thread and not a interface sender thread, look to see if SMAT is showing the same thing and let us know.
Depending on your findings will determine the next fork in this conversation.