Solution ID: prim80607
Unable to assign a valid relationship between two Start Milestones in P6 6.2 Web Access.
Status: Reviewed
Version(s): 6.2, 6.2.1

Problem: Unable to assign a valid relationship between two Start Milestones in P6 6.2 Web Access.
Problem:

“Selected Relationship Type is not Valid for this activity” when editing a relationship for a milestone.
Fix: This known problem in P6 Web Access has been corrected in P6 Web Access 6.2.1 Service Pack 1. To download the latest Service Pack for P6 Web Access 6.2.1, see: 

Solution ID: prim82785 ”What are the latest Service Packs for Primavera version 6.2.1?”
Fix: WORKAROUND: 

Create the valid relationships in the Gantt Chart.