Problem connecting to O365

We're having a strange issue with Outlook 2013 and Office 365 accounts

We have multiple Windows 7 PCs in the office, and all of them were set up by connecting Outlook to their Office365 mailboxes using autodiscover - which worked perfectly. Some have just one mailbox and others have access to one or more shared mailboxes - this done by giving the user the rights to the mailbox and the mailbox automatically gets pushed out to the user's Outlook.

However, we added rights to a shared mailbox for a user recently and it didn't appear on their Outlook. We logged them onto another PC and Outlook picked up the users mailbox AND the shared mailbox correctly - so we can assume there's nothing wrong with the Office 365 side of things.

Back on the 'problem' PC we deleted the Outlook profile and recreated it, then tried to re-add the mail account...