Maybe you used the wrong details when adding the company.
Make sure that the details you are using are still valid (these may lapse), watch out for typing errors and check that you are using the right details (customer number / account number / contract account etc.)
You will find the necessary information via our companies page.
If you are 100% sure of the entered details, and they are still not accepted, then you need to contact the company itself (or your employer in the case of salary documents).