As the life of Outlook's Social Connector winds down and SharePoint deprecating the server-side functionality for the SharePoint Social Connector, the SharePoint provider is no longer working in Outlook. Anyone still using the People Pane with an Exchange account may see a yellow banner saying "Unable to log in to: SharePoint. Click Here to log in."
To remove this message, users can open the Social Network Accounts dialog (View tab, People Pane, Account Settings) and delete the SharePoint account by clicking the X icon. However, this may result in another yellow banner that reminds the user to configure the SharePoint provider.
To remove the yellow bar completely, users or their administrator need to set a registry key to disable the SharePoint provider.
If you don't want to edit the registry yourself, I have a ready to use registry file available: Disable SharePoint Connector