Some Yahoo! Small Business customers have reported errors when attempting to access their Yahoo! Business Mail accounts when they login to the Yahoo! webmail interface and switch to their Yahoo! Business Mail account when using Internet Explorer 9.
Our engineers are aware of this issue and are working to resolve it as early as possible. In the meanwhile we request customers to access their business email via a different web browser such as Mozilla Firefox or Google Chrome
We apologize for any inconvenience this is causing.