Cannot add kinematics to End Item top-level because Start Modeling command is not active.
Solution
Add a Kinematics dataset to the top-level Item with a KinematicsRelation selection.
Adding the Kinematics dataset with the proper relation solves the issue.
Notes and References
Hardware/Software Configuration
Platform: INTL64
OS: window
OS Version: 764SP1
Product: TECNOMATIX
Application: PROCESS_SIMULAT
Version: V13.1
Function: BACKBONE_INTEG
Ref: 001-7645214