When filing to HMRC, you may encounter the below error message:
This error message comes directly from HMRC's server and unfortunately, it is one of the few scenarios we can't check when completing a test submission. This error message usually occurs when the UTR entered doesn't match what is expected. This can mean the UTR is correct but not being used for the correct service (e.g. you have declared a partnership UTR on an individual tax return instead of the individual's UTR).
When coming across this error, we recommend locating a HMRC document with the UTR issued as the reference for the client or logging on to the government gateway (if you are an agent and have a 64-8 in place you can do this too) to confirm the UTR listed for the entity.
If you have checked the details and you believe you have the correct UTR, user ID and password, it could be an issue with the UTR being blocked. To check this, you would need to contact HMRC on 0300 200 3600 (International: +44 161 930 8445) to discuss this further.