I have a sharepointOnline-site with a document library. All kinds of users (both internal/external and members/owners/visitors) can access the doclib and open documents in the browser-version of Office. Anyone who is logged in to the site can simply open the document in webApps with a single click.
When using the desktop Office-client to open the same document you prompted with a login dialog (this is understandable, the desktop-app might not be able to share the browser's session cookie). Internal users (users within the current organisation) are able to log in just fine, but external users (connected via hotmail or outlook) are told that they are denied access. After entering your username and password in the windowsliveId login, you get the following error dialog:
"Error - Access denied -You are not a member of this site. Sign in as a different user / Go back to site"
The access is denied for all external users no matter if you're opening the document as read-only or as editable. This does not occur for any in-organisation users.
I've looked around the sharepointOnline-administration panel and couldn't find any settings that would relate to this. The most obvious suspiscion would be that this is caused by sercurity settings in the desktop Office-client. Any idea which one?