Task list object cannot be processed with activity type &

What causes this issue?

You can process most task list objects with the activities "create",
"change" and "delete". However, you can only use the activities
"create" and "delete" for certain task list objects, such as the
material allocation to task list and component allocation. You cannot
use the activity "change" with these task list objects.

How to fix this error?

If you want to change the object without using the activity "change",
delete the object first and then recreate it.

Error message extract from SAP system. Copyright SAP SE.