When you login, we create a Named Credential in Salesforce that accesses the refresh/access tokens from Creditsafe via mylogin. If you have logged out and the same browser tries to login, an error occurs as the Named Credentials we’re trying to create (in Salesforce) already exists. 

To resolve follow these steps. Go to Salesforce Setup:

• Setup > Security > Named Credentials 
• Delete the existing named Credentials with the label Creditsafe
• Once credentials have been deleted, please go back to the settings and log back in