Svein and Reinier,

Thanks for replying to my query and for your suggestions. Sorry for not being quick to reply to you both - I'm travelling at the moment, with intermittent access to broadband. The first thing to say is that the problem hasn't recurred. I have also borrowed a netbook, and set up Skype on it, so now I can run the netbook and my laptop next to each other.

Short story - perhaps this was a wild goose chase; there doesn't seem to be any interaction of the kind I was suspecting. Either there was something odd going on with my son's computer (possible - he's a developer) or it was just one of those things.

I suppose I was thinking about port conflict, but didn't know how Skype acted: the link you sent was helpful, Svein, so were your comments, Reinier. I am very confident it wasn't a CPU/memory resource issue - my laptop was performing normally in every other respect; I had Firefox open at the same time and that didn't show any reduction in performance.

Reinier wrote:
"Try running a tool like Sysinternals TCPView and then start up your
application. Does it start listening on ports, possibly blocking inbound
connections (if you have listening ports open to the internet at all,
which you didn't mention).

Monitor CPU/memory usage and see what happens.

Try calling the Skype echo service while your application is running.

Try calling somebody again on Skype and let people call you while the
application is running."

I haven't had time to try TCPView yet, but I will, just out of interest. Over the next few days I'll double-check with your other suggestions in as many combinations as possible, but I'll only report back if I find anything definite and repeatable.

Again, thanks to you both.

Rob