From the CAS Webpage:
The portion of the Rosenberg and Guszcza textbook, previously used as the source for the multicollinearity material on Section C of Exam S, is no longer available free-of-charge for CAS candidates via an online link. As a result the Spring 2016 administration of Exam S will not include any questions on multicollinearity. This is a temporary change made to recognize the loss of the free access to a portion of the Rosenberg and Guszcza textbook. Fall 2016 and subsequent exams may include questions on multicollinearity.
The portion of the Rosenberg and Guszcza textbook, previously used as the source for the multicollinearity material on Section C of Exam S, is no longer available free-of-charge for CAS candidates via an online link. As a result the Spring 2016 administration of Exam S will not include any questions on multicollinearity. This is a temporary change made to recognize the loss of the free access to a portion of the Rosenberg and Guszcza textbook. Fall 2016 and subsequent exams may include questions on multicollinearity.
Multicollinearity, Exam S Syllabus