I changed my password via the web interface. And now I can\'t run any command that requires authentication. Password is using plain ASCII, nothing fancy, no Unicode, weird non-p
I had this same problem after changing the password, and I found it was because I was managing multiple accounts with the heroku-accounts gem.
I removed the account setup in heroku-accounts and then re-added it, using the new credentials to authenticate. Things then started working as before.
It seems that the authentication details stored in the heroku-accounts gem somehow override those you apply via the command line. Anyway, this worked for me.