Thanks for your comments, sWORDs.

In avSourceSendData() if the socket isn't created and connected, avSourceInitSocket() is called which defines the onConnect function. When (or if) the socket is connected successfully, avSourceSendData is called again: this time the command should be written to the socket.

Further investigation suggests the delay is occurring as the socket tries to connect. This occurs in a stripped-down system with 1 Pronto and nothing else trying to tie up the port on the GC-100. I'm going to look at enforcing a delay between the various TCP socket commands.

Andy