Fixing the "Submission Blocked" Error — Tax Computations Out of Sync
If you see this message when trying to submit your CT600 to HMRC:
> Submission Blocked > Your tax computations are out of sync with the reviewed CT600 period. Please go back and click "Preview & Submit" to regenerate your documents before submitting.
This is a safety check, not a data error. It means the CT600 documents need to be regenerated before submission — your data and any payment are already saved.
Why Does This Happen?
This message appears when the tax computations were generated at an earlier point and something has since changed — for example, if you submitted your Companies House accounts separately before submitting the CT600. TinyTax detects the mismatch and blocks submission to make sure what goes to HMRC is current.
How to Fix It
- From your dashboard, click Start Filing ▾ next to your company
- Select Continue on your in-progress filing session
- Click through Preview & Submit — this regenerates your tax computations (takes about 30 seconds)
- Once preview completes, the Submit Corporation Tax to HMRC button will become available
Common Questions
Will I be charged again?
No. Regenerating documents does not trigger another payment. Any payment you have already made is saved against your filing session.
My accounts are already accepted — do I need to resubmit them?
No. Going through Preview & Submit only regenerates the CT600 tax computation documents. Your Companies House accounts submission is unaffected.
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