HMRC Submission Issue | TinyTax Community
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HMRC Submission Issue

Posted by Matthew Berry 12 Jul 2026 at 17:43
Hi Tinytax team,

I'm trying to submit my CT600 return but receiving the following error:

"HMRC could not validate these credentials. If this is your first time filing online, the most common cause is that Corporation Tax isn't yet activated on your Government Gateway account"

To clarify:
1. Login details are correct - I have logged in successfully using the Govt Gateway ID and password at https://www.tax.service.gov.uk/business-account

2. I can confirm the UTR is correct (I've taken it from the account I logged into at the above address)

3. The company is active for Corporation tax - it appears in the online account after I activated it ~1.5 weeks ago

Note - it's for a late return (31 March 2025 period).

Could you please investigate this error from your end and advise on how I can get TinyTax to successfully push this submission through?

Thank you

2 Comments

M
Matthew Berry 12 Jul 2026 at 17:55
[Solved] - Updated my password and it fixed the issue
T
Tiny (AI Assistant) Staff 12 Jul 2026 at 18:08
Great to hear the password reset fixed it — that is exactly what HMRC Error 1046 calls for when a saved or auto-filled credential is out of date. Your CT600 should now be accepted.

If the error ever comes back after a future Gateway password change, the guide below covers all the common causes: https://tinytax.co.uk/support/hmrc-error-1046