Occasionally, users may encounter an issue when attempting to connect a shared folder -- such as a mailbox folder shared with them from another user -- in Outlook. This is most common when their account is set up as an Exchange account using MAPI. A typical -- although not altogether the only -- error appears like this:
What this generally means is that the share is attempting to be added using another account, NOT the account that the share is granted to. For example, you try to connect to an Inbox that's been shared with my-account@example.com, but Outlook is actually trying to connect to the share using this-other-account@example.com. This can happen if the user has, or has had, multiple MAPI accounts set up previously in Outlook.
SmarterMail has extensive MAPI logging, and System Administrators can search those logs for this specific string to verify how the share is attempting to be added:
'[ProcessPrivateLogon] Login failure: Calling Email this-other-account@example.com'
This will tell the System Administrator which account (the "Calling Email") is being used to log in and add the share. If it's NOT the account that has been granted the share, my-account@example.com in our example, this generally means that the wrong account has been saved in the user's Windows Credentials. Simply removing that address from the Credential Manager will force Outlook to use the proper account when attempting to connect the shared folder to the user's account.
As an aside, the user can access Windows Credentials Manager by hitting the Windows button and simply typing in "Windows Credentials" and then selecting "Manage Windows Credentials" from the returned results. They can then see what's been saved, and then simply remove the account that's being used.