Tasp If I run your code with my local IP (localhost does not work) it sends the initial message but since I don't send a response it seems to stop. If I remove the read part from the loop it works perfectly well and the ten messages are sent.
I have one PC running your code and the other PC running UDP Test Tool as host with the IP set to the machines local IP and the port set to 55000. But as I said at the moment I can only go one way.
Firewall is not an issue for me as I completely disable when trying to interface externally, internally it should not affect it. However I've tried with it disabled with the same result.
If I used TCPView (sys internals), it doesn't show an open port though?