Direct OAuth with the Yahoo! Messenger IM SDK: "403 Forbidden" response
I am using Direct OAuth with the Yahoo! Messenger IM SDK with PLAINTEXT encryption in my application to obtain the PART token for user sessions.
The problem: with most Yahoo! accounts it works fine, but with some accounts my app consistently gets infamous "403 Forbidden" response with "The user must manually login using a web browser on http://login.yahoo.com".
These users have no problems logging in via browsers though. Nothing in the account info indicates that anything is wrong with the account or blocked for application access. Removing all apps from "Manage App and Website Connections" to re-authenticate the account for third-party access doesn't help either.
Any suggestions? Anything on the Yahoo! side which is hidden from account owners need to be set or reset to enable them for IM app access?