Class for project summarization has not been generated

What causes this issue?

To be able to classify projects using the classification system, you
must first:
select the characteristics that are active in your system
generate the characteristics that you selected
generate the class in which these characteristics are to be included
You do this in Customizing under <LS>Choose and generate
characteristics</>.

System Response

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

How to fix this error?

Generate the class for project summarization. To do this, go into
Customizing for the project system and process <LS>Choose and generate
characteristics</>.

Error message extract from SAP system. Copyright SAP SE.