In Framework Manager, when attempting to define a relationship between a dimension and a query subject, or a dimension and another dimension, the relationship option is disabled (greyed out).
Defining a relationship on a dimension has never been recommended but was possible in earlier versions of Cognos BI. Experience has determined that relationships on dimensions cause more harm than good, so the ability to do so has been disabled in version 10.2.1 and higher.
Resolving the problem
Define the relationship between query subjects instead.