Box for Salesforce - "The Box Service Account Has Not Yet Been Set Up"

When trying to access any record in Salesforce, all users are seeing the following error message:

Cause

This error is caused when either:

• The Box Service account has not been set up
• The Box Service account has been linked to the Box User account

Resolution

If the Box Service account has not been set up yet:

• First set up the Box Service account according the the installation article.
• If an account other than the Box Service account is currently linked, you can take a look at how to change the Box Service account

If the Box Service account was linnked to the Box User account:

• First remove the Box Service account from the Box User settings
• Setup the Box Service account per the links above