What do you know about the agent from which these events are being received? If this agent is not a legitimate agent, I would recommend you remove it from your Authentication Manager configuration. AM will simply discard the "log request" protocol from an unknown agent.
If the agent is a well-known agent, I would check if some automated process is attempting to send data to the login interface at the agent. The "syntax error" log is generated by agents after experiencing some number of authentication attempts with passcode data that the agent identifies as not possibly being a passcode. For example, a passcode longer than 16 character or containing unsupported characters.
I would login to the agent generating the log event, enable verbose agent logging (or network-level data capture with something like "Wireshark"), and examine those logs for additional clues as to the source of the problem. Even if you do simply remove the agent, I would probably investigate the IP address, what is running it,and the system from which the network traffic is being sent.
