Some task lists cannot be changed, since you do not have authorizations

What causes this issue?

You want to change task list objects. However, you are not authorized
to change some of these task list objects. The reason for this can be
as follows:

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

You have entered a change number whose change master record forbids you
to edit the objects.
You have entered a key date and the task list has a history
requirement.
Your authorization profiles do not allow you to edit the corresponding
task lists.
According to the change rules you have to enter a change number if you
want to edit the task list.

System Response

You cannot change the objects.

How to fix this error?

If necessary, check the change number entered.
If necessary, enter a suitable change number instead of a key date.
Check the <DS:TRAN.SU53>"Display Check Object if Not Authorized"</>
screen where you can see which authorizations you lack for which task
lists. Ask your system administrator to change your authorization
profiles if necessary.
Check the change rules for the task list and enter a change number if
necessary.

Error message extract from SAP system. Copyright SAP SE.