I am also getting the same error message on my new nexus s that I received 2 days ago... "general login error, unable to add account" some of the things I have tried include:
I can log in with my laptop, and on the mobile web browser
I can log into the app though with a different yahoo account but not the main one I use,
I can access the account from a different droid (my touch 3g) using the exact same app version and same yahoo account.
I have power cycled phone
cleared cookies
cleared cache
cleared history,
called the service provider
contacted yahoo mobile tech support via email
no special characters in password
tired adding @yahoo and leaving it off the account login
changed yahoo password
same issue with same yahoo account and same phone using yahoo messenger app
All attempts to log into my primary yahoo account via the yahoo mail app on my new phone have failed . I am out of ideas here and I'm hoping someone else has a brilliant idea they can offer :'(