Maybe your IP block is on their ddos-prevention blacklist currently. I don't have any insight into how Prolexic works but seem to recall some folks being prevented from connecting as a side effect of the anti-DOS system before.
Alternatively, some relays in between you and gox may simply be having issues at the moment.
I was worrying about that too. But I am a 100% clean trader, the worst I have done is letting clarkmoody and bitcoinity on 24-7, do those websites use my ip address to query the MtGox trade log? If it is so, they may block me for sending numerous request.