Check you have entered the correct credentials
Make sure your credentials are entered correctly. See Online Filing Passwords.You may have different credentials for CT and SA filing so make sure you have entered the correct ids. You must ensure you are using valid agent credentials and not client credentials. You do NOT need valid authorisation for the client to file (e.g. 64-8), but you must be using valid credentials for the correct service.
Please make sure you are using the correct id and password for the return you are filing. You cannot use an individual’s id and password to file a partnership or trust return – they must have their own id and password.
Check that you have entered the correct UTR
If the UTR is incorrect you should unlock the tax return submission before changing it.