Because of a hardware problem at one of Yahoo’s colocations, a number of Yahoo! properties are having technical issues. Yahoo! Groups users are being slightly affected because the Yahoo! Calendar (which Groups leverages) is temporarily "read only" (meaning you can’t add new events).
In more positive news, we have pushed a fix to the problem which surfaced this week preventing moderators from being able to view images in pending messages (generally, we never push code on a Friday but this bug seemed severe enough to warrant it). Note that one element (the "preview" link) on the edit pending message page is still broken, but we wanted to get this out regardless so that moderators who needed to view images before approving them could begin doing so immediately.
Thanks for your patience,
Yahoo! Groups Team