Transfer status does not allow deletion

What causes this issue?

The project or project structure has already been transferred to
accounting. You can no longer delete the project or any individual
project elements from the project structure for consistency reasons.

System Response

The system issues an error message and will not allow you to continue with this transaction until the error is resolved.

How to fix this error?

You can now only archive the project.

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.