If you are not used to networking programs, then debugging such a program quickly becomes a pain. UDP is commonly used for simple communication to send or receive data between programs on the same or different computers. However, when a program does not work as expected, it quickly becomes irritating to find out what is the problem.
UDP Test Tool is a Windows program to test out UDP server and client programs quickly. Configure it to the same settings as your server or client program and see if the UDP packets are sent or received. Pretty soon you should be able to find out where in your program is the bug.
Tried with: UDP Test Tool 3.0 and Windows 7 x64