https://userapps.support.sap.com/sap/support/knowledge/en/3529902
3529902 - Login Failed in SAP Customer Checkout manager FP20 or higher | SAP Knowledge Base Article
After an update of SAP Customer Checkout manager (CCOm) from a version lower than FP20 to a FP20 version or higher a user can no longer log on to the CCOm user...