Good news - I can see your Corporation Tax return (CT600) for CLB CLEANEQUIP LTD was successfully submitted to HMRC at 14:45 today and has been accepted.
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Tina Connell1 May 2026 at 22:56
Hi, I am a first time user of Corporation tax, I have a gateway account but when I get to submit I have error message saying HMRC credentials not accepted, can anyone help please?
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Tiny (AI Assistant)Staff2 May 2026 at 06:01
Hi Tina — happy to help.
"HMRC credentials not accepted" at the submit step is HMRC error 1046. It's a generic authentication failure from HMRC, and it almost always comes down to one of three things:
1. The Government Gateway User ID and password don't match what HMRC has on file (often a typo, or using the wrong account).
2. The Gateway account exists but isn't enrolled for the Corporation Tax service for this specific company.
3. The 10-digit Company UTR you entered doesn't match the one HMRC has linked to the company.
The quickest way to rule them out is to log in to HMRC directly at https://www.tax.service.gov.uk/business-account using the same User ID and password you're entering on TinyTax. If you can sign in and you can see "Corporation Tax" in the list of services for the company, your credentials are good — in which case it's almost certainly the UTR.
A few specific things worth checking:
- Make sure you're using an Organisation Government Gateway, not an Individual one. Self Assessment / personal Gateways can't file Corporation Tax. If you only see Self Assessment in your services list, you'll need to set up an Organisation account separately.
- Enter the User ID with all 12 digits, no spaces.
- The Company UTR is 10 digits with no spaces or hyphens — it's on HMRC's "Notice to deliver a Company Tax Return" letter, addressed to the company at its registered office. It's not the same as your personal UTR.
- For brand-new companies (incorporated in the last few weeks), HMRC sometimes hasn't finished registering the company for Corporation Tax yet, so CT won't be available on the Gateway. In that case you'll need to enrol for CT and wait for the activation code HMRC posts to your registered address (usually 7–10 working days).
Full walk-through with screenshots and the most common causes is here: https://tinytax.co.uk/support/hmrc-error-1046
If you've checked all of the above and it's still being rejected, reply with: (a) confirmation you can sign in at the HMRC business tax account link above, (b) whether Corporation Tax is listed there for the company, and (c) the company name/number — and I'll dig in further.
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"HMRC credentials not accepted" at the submit step is HMRC error 1046. It's a generic authentication failure from HMRC, and it almost always comes down to one of three things:
1. The Government Gateway User ID and password don't match what HMRC has on file (often a typo, or using the wrong account).
2. The Gateway account exists but isn't enrolled for the Corporation Tax service for this specific company.
3. The 10-digit Company UTR you entered doesn't match the one HMRC has linked to the company.
The quickest way to rule them out is to log in to HMRC directly at https://www.tax.service.gov.uk/business-account using the same User ID and password you're entering on TinyTax. If you can sign in and you can see "Corporation Tax" in the list of services for the company, your credentials are good — in which case it's almost certainly the UTR.
A few specific things worth checking:
- Make sure you're using an Organisation Government Gateway, not an Individual one. Self Assessment / personal Gateways can't file Corporation Tax. If you only see Self Assessment in your services list, you'll need to set up an Organisation account separately.
- Enter the User ID with all 12 digits, no spaces.
- The Company UTR is 10 digits with no spaces or hyphens — it's on HMRC's "Notice to deliver a Company Tax Return" letter, addressed to the company at its registered office. It's not the same as your personal UTR.
- For brand-new companies (incorporated in the last few weeks), HMRC sometimes hasn't finished registering the company for Corporation Tax yet, so CT won't be available on the Gateway. In that case you'll need to enrol for CT and wait for the activation code HMRC posts to your registered address (usually 7–10 working days).
Full walk-through with screenshots and the most common causes is here: https://tinytax.co.uk/support/hmrc-error-1046
If you've checked all of the above and it's still being rejected, reply with: (a) confirmation you can sign in at the HMRC business tax account link above, (b) whether Corporation Tax is listed there for the company, and (c) the company name/number — and I'll dig in further.