Cannot change task type

What causes this issue?

You can only change the request type if this is permitted by the type
of objects in the request.
The requirement is not met in this case.

System Response

The function terminates.

How to fix this error?

In the hierarchical request overview, choose the function
<LS>Request/task</> -> <LS>Overall check</> -> <LS>Check request
consistency</>.
If the task contains errors, a list of the incorrectly assigned objects
appears with detailed information on how the errors can be corrected.
For more information on the Transport Organizer functions, see the SAP
Library under <LS>BC - Basis Components</> -> <LS>Change and Transport
System</>.

Error message extract from SAP system. Copyright SAP SE.