This issue can be caused by one of two things.

The first is where you haven't previously been checking for the Companies House responses (using Efile / check for response) and so the backlog of receipts is too many for the system to allow for any further. To resolve this you need to go to Efile / clear responses and for this submission confirm with Companies House that they have been received. Moving forwards you then need to try using Efile / Check for response on a more regular basis.

The second cause of this error is where the details for the company you are filing does not match the Companies House servers. This can be anything such as the company name logged on the register has Limited in full but the submission file shows it as Ltd.