On my MacBook, "there was an error".

[SamIAm]

I've had my macbook for a few months now, and it's great. (I don't have to worry my pretty little head over all those complicated mouse buttons.) However, recently I've been unable to connect to any wireless networks outside of work and home. When I try at a coffee shop or a friend's house, I get the message "There was an error joining the AirPort network 'xxxxx'." (Note that Mac doesn't tell me what error, just that there was an error.)

This doesn't happen at either my home or work wifi, so it's not such a big deal; I connect fine to both those secure wireless networks, but if it's a new network (secure or insecure) I'll almost always fail. (I have connected a couple times successfully. ~20%.)

Another point that might help: recently MacStumbler has stopped working too. It used to find my card and show me all the networks around. Now it just searches and searches with no sign of recognition.

Any ideas?