Let me share insights to help you file your tax return, @AJDOYLE.
Select valid date error message happens because QuickBooks will no longer prepare annual accounts dated on or before April 1, 2023, or accounts exceeding 365 days old.
Since your filing a return that falls before the date and year after is no longer supported in QuickBooks Online (QBO). You can consider directly filing your form through His Majesty's Revenue and Customs (HMRC) and visit the HMRC website to reach out to their support to further assist you in filling out your tax return.
Once you're ready to file the latest period of your CT600 form, refer to this article to further guide you with the steps in preparing and submitting your Corporation Tax return in QuickBooks Online: File your Corporation Tax return.
I'm always here to assist you with any other questions you have about tax forms. Take care.