• BeginString(8) is not the first tag in a message or is not of the format 8=FIXT.n.m.
• BodyLength(9) is not the second tag in a message or does not contain the correct byte count.
• MsgType(35) is not the third tag in a message.
• Checksum(10) is not the last tag or contains an incorrect value.

If the MsgSeqNum(34) is missing a Logout<5> message should be sent terminating the FIX Connection, as this indicates a serious application error that is likely only circumvented by software modification.