UDP hanging on Rx 10K+ filesize... 1k packet xfers

Apologies if this has been reviewed to death...

I have a system that I am implementing on a cyclone 3 w/niosiif - there is a modified UDP socket server running, this services a system in which there are 64 byte command packets and larger (at the moment 1024 byte fixed size) data packets streaming to/from the board. Initially there is a "DataXfer" command telling the software that the next xfer is a burst of data to a specific frame buffer. The data then bursts to the specified buffer that is passed in

bytes_read = recvfrom(sock, Data.pRX_wr_pos, UDP_PORT,0,(struct sockaddr *)&client_addr, &addr_len);

All xfers are responded to by an "ack" frame before the next frame comes...

My issue is that I get several packets (1-6) of data in before the system hangs and I am wondering what I can do about it - I do read that people have this system working... I felt that with the "lock-step" method of transferring data I could avoid buffer overruns, etc... not certain why the hangs are happening - any thoughts are appreciated...

Thanks - crayner