Inclusion is not possible; proj. type does not permit selected elements

What causes this issue?

One or more of the project elements that you have selected for inclusion
are not permitted for projects or project templates with the current
project type. The corresponding project element category has not been
activated for this project type in Customizing.

System Response

The selected project elements are not included.

How to fix this error?

RESET N1
Check the project type assigned to your project or project template.
To display the project type, open the <LS>Detail</> subview of the
project structure and access the <LS>Basic Data</> tab page of the
project definition.
Check which project element categories are permitted for this project
type.
You can find this information in Customizing for <LS>SAP Portfolio and
Project Management</> under <LS>Project Management</> -> <LS>Structure
</> -> <LS>Define Project Types</>. The relevant settings are displayed
on the <LS>Details</> screen for the project type in the screen section
<LS>Project Structuring</>.
Take one of the following actions as required:
In the <LS>Include</> function, select only project elements that are
permitted for the current project type, and include them.
To include elements from a subtree containing both permitted and
forbidden elements, proceed as follows:
a. Manually create the root element of the subtree in the target project
or template.
b. Select the root element and include the permitted subelements from
the source project or template.
On the <LS>Basic Data</> subview of the project definition, assign a
project type which permits all required project elements, and include
the elements.
Change the project type in the Customizing activity <LS>Define Project
Types</> to allow all required project element categories. Refresh your
project or project template and include the elements.

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.