Microsoft Updating SharePoint Online to Service Update 1

SharePoint Online (part of Office 365) has the ability to allow external users access to the site via Microsoft Live ID.

While attempting to accept the email invitation, we encountered the following error:

After doing a bit of research (and contacting technical support) we discovered Microsoft is deploying Service Update 1 to SharePoint Online. It appears Service Update 1 will include a number of enhancements to SharePoint but is causing issues with Windows Live ID login at the moment.