Dataloader cannot process nested messages and the below error message is seen in Dataloader logs
14:50:34 ERROR: Message.OpenProperty(R_RTF_COMPRESSED):
14:50:34 Low level error: 80004005
14:50:34 Context: 00000501
14:50:34 ERROR: Unable to get message checksums:
14:50:34 Email2.get_Body
14:50:34 Error 0x80004005