This is not a question, but a solution if you come a cross "Submission Error" when submitting Corporation Tax using HMRC online services.
With introduction of new CJRS and Eat Out to Help out Schemes there additional fields to complete when you are doing online tax return.
So even if you complete the fields that are only applied to you there can be errors such as error code 4085, 4052. If your tax submission shows "Submission error" and shows the error codes it can be fixed by simply saying "Yes" to Eat Out to Help out Schemes question (even if this dosen't applied to you). Then when the form ask you how much you claimed type "0". Then resubmit the completed return.
Hopefully this could help someone like it helped me after few attempts.