HMRC Error 1046: Why Your CT600 Sign-In Was Rejected

HMRC error 1046 means HMRC did not accept the sign-in details sent with your Company Tax Return (CT600). HMRC turned the return away before looking at it. This response is not an acceptance. Your filing deadline still applies, and a rejected attempt does not prevent late-filing penalties. Your saved figures and documents remain available in Unfiled.

The message is deliberately vague. HMRC does not say which detail it rejected, so nobody can use it to guess valid user IDs. You have to find the cause yourself. In practice there are only a few, and you can check most of them in about ten minutes.

Pause before trying again. Each failed attempt counts as a failed sign-in on the Government Gateway account. Several in a row can lock the account for a while, and a locked account keeps returning 1046 even after you have fixed the real problem. Work through the checks below first, then make one careful attempt.

The one test that answers most cases

Open the HMRC business tax account in a private browser window. Choose Sign in with Government Gateway (not GOV.UK One Login) and type the exact user ID and password you entered in Unfiled. Do not let your browser fill them in.

What happens next tells you where to look:

Check 1: You used the right kind of login

CT600 returns sent by software are still checked against Government Gateway credentials. GOV.UK One Login, the newer email-based sign-in, does not work for software filing, even when it opens the same HMRC account on the website.

• A Government Gateway user ID is normally a 12-digit number. If what you typed is an email address, it is a One Login ID.
• The Gateway password is separate from the One Login password. Changing one does not change the other.
• Your Unfiled password, UTR, company number and Companies House authentication code are all different things. None of them belongs in the HMRC sign-in fields.

If you have lost the Gateway user ID or password, follow our Government Gateway sign-in recovery guide.

Check 2: The account can file for this company

Signing in proves who you are. It does not prove the account may file for the company. The Government Gateway account must have the Corporation Tax service added for this company's UTR, and that service must be activated.

To add it:

1. Sign in to the business tax account with the Gateway user ID.
2. Choose Add a tax, duty or scheme, then Corporation Tax.
3. Enter the company's UTR and the details HMRC asks for.
4. HMRC posts an activation code to the company's registered office. Allow up to ten days for it to arrive.
5. Enter the code in the business tax account before it expires.

You cannot file online until the service is active, and the code cannot be emailed. If the deadline is close, request it straight away.

Use the company's own Gateway account. A former accountant's login, or a personal Self Assessment account with no Corporation Tax service, will be rejected.

Check 3: The UTR is the company's, not yours

This is the cause people most often rule out too early. A company has its own 10-digit Corporation Tax UTR. A director who files Self Assessment has a personal 10-digit UTR. They look the same, and HMRC will not tell you which one you sent.

Compare the UTR shown under Corporation Tax in the business tax account, digit by digit, with the Corporation Tax UTR field in the company details step of your return in Unfiled. Enter the ten digits only, with no spaces or letters. If you are not sure where to find it, see how to find your company or personal UTR.

Correcting a wrong UTR changes the return itself, so you will review and confirm the return again before submitting. The sign-in retry described below is only for corrected Government Gateway details.

Check 4: The account is temporarily locked

If you tried several times in quick succession, HMRC may be refusing the account for a while regardless of what you send.

• Stop all attempts for at least a couple of hours.
• If you are unsure of the password, reset it through Problems signing in on the Government Gateway page, then sign in to the business tax account once to confirm the new one works.
• Then make a single attempt. If it still fails, leave it until the next day rather than retrying again.

Check 5: Your browser filled in an old password

Unfiled does not store your Government Gateway credentials. You type them for each submission and they are used only for that request. Your browser or password manager, however, may silently fill the fields with a password you have since changed. The password then works on HMRC's website, where you typed it, but fails in the filing form.

Clear both fields and type them yourself. If your password manager keeps an old entry for Unfiled, update or delete it.

Trying again in Unfiled

Once you have found and fixed the cause, open the return in Tax filing. When HMRC rejected only the sign-in and your corrected Government Gateway details are ready, the Payment and filing step offers an explicit retry. It resends the same return you already reviewed and paid for, and Unfiled checks it again before anything is sent.

If no retry option appears, contact us through the contact form before submitting again. We will check what HMRC returned for that attempt.

If you still get 1046

If the business tax account shows Corporation Tax as active, the UTR matches and a typed password still fails, call HMRC's Online Services Helpdesk on 0300 200 3600. Ask them to confirm that the Gateway user ID is enrolled and active for Corporation Tax on the company's UTR.

If an HMRC adviser says software sign-on is "successful" but the return is still rejected, the password is fine. Go back to Checks 2 and 3: the account is signing in, but not with access to the UTR on the return.