For some reason, yet to be discovered, the client hits on port after port until they are all jammed up. Next time this happens try connecting to the Net on any other program. You won't be able to.
To clear it, just close the client , then restart it.
I have 18 machines running right now and I have to do this between 10 and 20 times a day.
I have found that my P4s do it more often than my AMDs. But that could be because they produce twice as much.