Hi J. Dem
This error is displayed when you are using the wrong login details to access the Customs Declaration Service. (CDS) or your EORI has already been subscribed to another account.
Please use the User ID and Password you created when you subscribed to CDS.
You may need to speak with colleagues to find out who has subscribed on behalf of your company.
If you are unable to locate the correct login details you should contact the Online Services Helpdesk:
Technical support with HMRC online services
They will be able to complete security and assist you in recovering these.