I'm having trouble with guest/external user access to SharePoint Online. I've run into the same problem with both my MSDN Office 365 Developer account, and a trial of the Small Business Office 365 offering.
I am trying to give an external user with a Microsoft Live User ID read privileges to my site and/or a .odc file in a data connections library on my site. The MS Live User ID isUser@MyDomain.com, but it is registered as a MS Live ID that I use to access my XBox services, SkyDrive etc.
I've tried sharing the .odc file with this email address. I've also tried adding the user (email addressUser@MyDomain.com) as a member of the "Vistors" group, "Excel Services Views" group, and even the "Members" group.
This user gets the email invitation. The login to the Live ID service is successful, but then I get an error message that they're not a members of the site ... even when I've tried to add them to the "Members" group.
How can I make it so that users with a valid Live ID can (and must) log in and use .odc files on my SharePoint Online site?
What I'm ultimately trying to do is to host some .odc files on the SharePoint site that have the connection info for an Analysis Services datapump hosted on a remote webserver. External Users need to connect to this datapump/SSAS, but I want to protect the .odc file with SharePoint authentication. If I didn't have to use SharePoint, I wouldn't. However, as far as I can tell, it's only by using SharePoint and Excel Services that I can have Excel clients point at a hosted .odc file rather than have a local copy of the .odc file.