09:45 AM PST: Errors Accessing Mail Messages – New Yahoo! Mail
Some Yahoo! Business Mail users may encounter an error when attempting to read individual email messages while using the New Yahoo! Mail web page interface.
We are aware of this issue and are working to resolve it in a timely manner. As a workaround, users may change to the “Classic Mail” format by clicking the “Classic Mail” link in their Yahoo! Business Mail web mail page.
12:38 PM PST
This issue has been resolved.