'Valid credentials must be provided by the application principal.'
I got this error when I was developing a web page of registration form. It is on this line:
Guid dkey = Asi.Business.Common.DocumentSystem.DocumentKeyByPath("$/Common/Queries/Value Lists/ChapterList");
This error is gone after I login by 'manager'.
But since it is a new contact register page, it makes no sense to force user log in first.