Have you ever checked you Schedule Log and found an error Invalid Relationships for Milestones? This is due to the fact that Milestones depending on Start/Finish have certain relationships which are valid. We need to keep the following aspects in mind when we are using Milestones in our schedule.

1) Start Milestones can have:

FS, SS predecessors – Start Milestone should be driven by predecessor with a Start relationship hence the logical relationship for it is FS & SS.
SS, SF successors –  Start Milestone should drive the successor with the start date hence the logical relationship for it is SS or SF.

Start Milestones should not have F->F or S->F relationships as Predecessors, or F->S, F->F as successors.

2) Finish Milestones can have:

SF, FF predecessors – Finish Milestone should be driven by predecessor with a  Finish relationships hence the logical relationship for it is SF or FF.
FS, FF successors-Finish Milestone should drive the successor after they finish hence the logical relationship for it is FS or FF.

Finish Milestones should not have F->S or S->S relationships as Predecessors, or S->S, S->F as successors.

Valid Relationships

  • The only valid relationship between 2 Start Milestones is a SS relationship.
  • The only valid relationship between 2 Finish Milestones is a FF relationship.
  • The only valid relationship from a Start to a Finish Milestone is a SF relationship.
  • The only valid relationship from a Finish to a Start Milestone is a FS relationship.
  • In the Client, FS is a valid relationship to all tasks. In the Web it is not as a predecessor to a Finish Milestone and as a successor from a Start Milestone.