3.4.4 Message Signature Functions
In the case of connectionless NTLM authentication, the SeqNum parameter SHOULD be specified by the application and the RC4 stream MUST be reinitialized before each message (see section 3.4).
In the case of connection-oriented authentication, the SeqNum parameter MUST start at 0 and is incremented by one for each message sent. The receiver expects the first received message to have SeqNum equal to 0, and to be one greater for each subsequent message received. If a received message does not contain the expected SeqNum, an error MUST be returned to the receiving application, and SeqNum is not incremented.