Outlook: Cannot expand the folder

Overview

When you try to add another mailbox to your Outlook Folders, Unable to expand the folder error occurs.

Solution (If appropriate)

Error seems to occur with corrupted .pst files. The solution to this error is to delete the Outlook profile from the Control Panel. 

1. Click on the magnifying glass icon located at the bottom left corner of your screen
2. Type in "Control Panel"
3. Click the icon called "Control Panel" to open it
4. In the search bar located at the top right corner of the Control Panel's window, search for "Mail" and click on it
5. Click on Show Profiles
6. Select the Default File, called "Outlook" and click on Remove
7. Once the profile is deleted, Open Outlook and Add the account back

Symptoms

When you try to add another mailbox to your Outlook Folders, Unable to expand the folder error occurs.

Error Code

Cannot expand the folder

Cause (If Known)

Possible corrupted .pst files