There are open CTS projects

What causes this issue?

You tried to close the project, but it contains CTS projects with open
transport requests, and can therefore not be closed.

System Response

Action cancelled.

How to fix this error?

Go to the '<ZH><ZK>Transport requests'</><AB></></> tab where you can
get an overview of active CTS projects and the status of their
transport requests.
The project cannot be closed until all CTS projects have been released.

Procedure for System Administrators

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

Error message extract from SAP system. Copyright SAP SE.