Project Detail Page issue

Hi guys,

My question is on Project Detail Pages. I 

I created a Page Detail Page and gave it a title. However, after capturing the details in the PDP form and then closing the form so my details could be saved and checked-in, I get the following error:

The error complains about the Project Number which is a field defined as mandatory on another PDP but not the current one.

What could be the cause of this?

Thanks.

Regards,

Kwazi