TCP Status - Syn Received

Can someone help me out with the meaning of an inbound connection where the TCP State is stuck and Syn Received? Yesterday, without any changes on my end. One particular outside IP address can no longer get to a server on my LAN. That particular IP can’t ping my outside connection or telnet, etc. No problems connecting from anywhere else. When I check Firewall Connections, I see the connection attempts, but it doesn’t get any further than Syn Received.

Does that indicate a problem on my end, or would it be upstream from me? Any clues where to start?
Thanks,
M

Have you checked your firewall rules?
Maybe the outside IP has been tagged with one of your rules and is dropping packets.
Look under IP / Firewall / Address Lists