You can lock planned dates and forecasted dates to protect them against update.
indicates an unlocked date, a locked (read-only) date.
Click in any Planned cell to lock all planned dates of the plan.
To unlock the locked planned dates, click at any planned date.
Select the milestone for that you want to lock the forecasted date.
Click in the Forecasted cell.
To unlock a locked forecasted date, click next to the date.