It runs ok until it gets to the receive_from and does indeed block as its not seeing anything at the socket, and no error occurs. Data is arriving at the socket as I can receive it using the windows recvfrom, which would also block until something is received. ----------------- Could you describe what goes wrong exactly? Note that receive_from "will block until data has been received successfully or an error occurs" http://tenermerx.com/Asio/asio-1.3.1/doc/asio/reference/basic_datagram_s ocket/receive_from/overload1.html This email has been scanned for all known viruses by the MessageLabs Email Security System. Systems Engineering & Assessment Ltd - Beckington Castle, 17 Castle Corner, Beckington, Frome, Somerset, BA11 6TA, UK is registered in England and Wales with the company number 2430846. The contents of this email (including any attachments) are confidential and may be legally privileged. If you are not the intended recipient of this email any disclosure, copying, distribution or use of its contents is strictly prohibited. You should notify the sender immediately and then delete it (including any attachments) from your system. Please help out the environment by only printing this e-mail if absolutely necessary - Thank You.