CT600 rejected by HMRC: what the error means and what to do next

By Max Szolcek, founder of Dormant Return. Last updated 17 September 2026

A rejected Company Tax Return is not a filed one, and it is not a penalty either. HMRC's Transaction Engine returns a numbered error explaining what it did not like. The numbers are the same whichever software sent the return, so this guide covers the ones a dormant or small company actually meets, quoting HMRC's own wording, and says what to do about each.

First: was the return evaluated at all?

HMRC's online filing service works in two layers. The Government Gateway checks who is submitting; HMRC's Corporation Tax system then checks what was submitted. Errors from the first layer mean the return was never opened. Errors from the second mean it was read and failed a rule. That distinction decides what you do next, so it is the first thing to look at.

Whatever the error, nothing has been filed. HMRC does not keep a rejected return, and the filing deadline has not moved: the penalty clock in late CT600 penalties for dormant companies keeps running until an accepted return replaces the rejected one.

Error 1046: the sign-in was refused

HMRC's text: "Authentication Failure. The supplied user credentials failed validation for the requested service." It is raised by the Gateway, not by the Corporation Tax system, so the return was not looked at.

It means the Government Gateway user ID and password either do not match, or match an account that is not set up for Corporation Tax on the UTR in the return. Common causes, in rough order:

A typo in the user ID or password. The user ID is up to 12 characters and is not your email address.
The wrong UTR in the return. A director's personal Self Assessment UTR, another company's UTR, or one wrong digit. The sign-in is checked against that exact UTR, so HMRC refuses it even when the user ID and password are right. We confirmed this on HMRC's test service in September 2026. If your details work on gov.uk, check this first: compare the UTR on the return with the one shown against Corporation Tax in the business tax account. Company UTR vs personal UTR explains how to tell them apart.
Signing in with GOV.UK One Login details. Software filing uses the Government Gateway user ID and password.
The Gateway account has never had Corporation Tax added, or the enrolment was never activated with the code HMRC posts out. See enrol for Corporation Tax online before you file.
A personal Gateway account rather than the company's organisation account.
A team member's sign-in that has not been given access to Corporation Tax. The account's administrator gives access under "manage account" in the business tax account.

With Dormant Return, a 1046 leaves the draft exactly where it was: paid, prepared, and ready to file again once the details are corrected. Because the return was never evaluated, nothing is refunded and nothing needs re-entering except the sign-in. If the UTR was the problem, the filing page shows the UTR on the return and lets you change it; the return is checked again and you file without paying again. After five failures in a row, filing on that return pauses for 5 minutes and we email you a short checklist (can you sign in on gov.uk, is Corporation Tax in the account, does its UTR match the return), partly so that a bad password cannot lock the company's Gateway account through repeated attempts. The return stays paid, so you can try again after the pause without paying twice. If you close the page to go and find the right details, we email a link back to the paid return after half an hour, and if it is still unfiled 24 hours after payment we close it and refund automatically (or 30 days, if you ask us to keep it while Corporation Tax is being activated on your account); do not pay for a second copy in the meantime. For tracking down a lost user ID or password, see find or recover your Government Gateway user ID and password.

Error 3001: HMRC read the return and found a problem

HMRC's text: "The submission of this document has failed due to departmental specific business logic in the Body tag." On its own this says nothing useful. It is a wrapper: the specific reasons come as a list of further errors inside the response, each with its own number and text, and those are what Dormant Return shows you on screen. The real message is always one of the codes below, or a message like them.

Error 1608: the UTR is not on HMRC's records

HMRC's text: "Unable to lookup taxpayer details." HMRC checks the 10-digit Corporation Tax UTR in the return against its own records and cannot find it. Almost always a mistyped or wrong UTR: a personal Self Assessment UTR entered by mistake, or the UTR of a different company. Filing under your own Government Gateway sign-in, a wrong UTR usually shows up earlier as error 1046 instead, because the sign-in is not set up for it. Check the number against an HMRC letter, and see company UTR vs personal UTR if you have none to hand.

Error 7752: the company number does not match the UTR

HMRC's text: "The CRN on the submission does not match the CRN for this Unique Taxpayer Reference." The UTR exists, but HMRC holds a different Companies House registration number against it. Either the company number was mistyped, or the UTR belongs to another company. Both numbers are on HMRC's letters to the company; check them side by side.

Error 3304: a return for this period already exists

HMRC's text: "Original return already received for this period." An original return for the same accounting period has already been accepted, perhaps by an accountant, or by an earlier attempt you thought had failed. Check the company's business tax account: if the period is shown as received, there is nothing more to file. Correcting an accepted return needs an amendment, which is a different kind of submission and not one Dormant Return makes.

Error 7782 and other period errors

HMRC's text for 7782: "The accounts start and/or end dates are not appropriate to this Accounting Period." The dates in the return do not line up with the accounting period HMRC is expecting. The business tax account lists each outstanding period with its exact start and end dates, and the return must match them. A first accounting period longer than 12 months is a classic cause, because HMRC expects two returns for it; see why HMRC expects two CT600s for a first period.

Rejected elsewhere? Dormant Return prepares and files a dormant company's CT600 and iXBRL accounts for £5, under your own Government Gateway sign-in, and refunds automatically if HMRC rejects the return. The error texts above are shown to you in full, with the return untouched, so a typo is a two-minute fix.

Start your return

Error 3312: a mandatory item is missing from the accounts

HMRC's text takes the form "Legal form of entity (bus:LegalFormEntity) is missing." The iXBRL accounts attached to the return lack a tag HMRC's joint-filing checks require. This is a software fault, not something you typed: the tags are generated, not entered. Dormant Return's accounts are tested against HMRC's own test service, so you should not see this from us; if you do, it is our problem to fix.

A fault on our side

Occasionally a filing fails before it reaches HMRC, for a reason in our own software rather than in your return. Dormant Return shows this as "Something went wrong on our side", refunds the payment automatically, alerts a person, and asks you to try again later. Nothing was sent to HMRC.

What happens to your money

With Dormant Return, every rejection except a 1046 sign-in failure ends the same way: nothing is filed, and the £5 (or £15 for the active-company return) is refunded automatically, usually reaching your bank within five to ten working days. You then start a new return with the detail corrected. The overall flow is in how to file a dormant company CT600 online.