This message indicates an issue with the security code. An Admin user may verify that the security code being used is listed as Active using these steps:
  1. Log in to the BBMS Web Portal
  2. Go to Account Management > Mobile Devices
  3. Verify the code being used says "Active"

If the code is active, the MobilePay user should log out of the app and then back in. If the code is Suspended or the user cannot log back in please see How to get a security code or add a new device for MobilePay?