Jack, I remember this being an issue a while back, but I thought it had been resolved. However ... I found this stashed on my imac. No idea why I kept it or where it came from.
Do you possibly have another device that is logged in to apple? iPad, iPhone, droid phone logged in to apple support or something? Another computer logged in to iTunes? Your own computer logged in to iTunes? (I'm trying to be helpful and think of everything that *might* be trying to send a password).
Anyhow, the suggestion was to log into the apple id page with a browser in order to verify the password. If the acct has been locked or something, it should show up when you get there.
https://appleid.apple.comThen sign out of ALL your devices to ensure that the old password is cleared and not stored incorrectly. A reboot on your devices might be good as well. Then try logging in to the app store again and see if that works.
You can also contact apple support and see what they have to say:
http://www.apple.com/support/appleid/I'm not a fan of the app store, but that's the only place to get some apps that I find right handy.
I do use 1Password to store all of my passwords, but I still have to launch that separately, copy my password for the app store and then paste it in. If 1Password does this seamlessly at the app store, I'd appreciate knowing how that works.