Action causes scheduling conflict because a linked task cannot move
The change that you're making results in a conflict between the task's dependency and the fixed date set for this task. When a task is linked in a project that is scheduled from the finish date, the successor task's start or finish dates drive the predecessor task's start or finish date. If the predecessor task is also constrained to a fixed date, the task dependency cannot be honored because the successor cannot drive the predecessor's start or finish. You can avoid this scheduling conflict by canceling this action with the Planning Wizard.
Go to Set a task start or finish date (constraint) for a task for additional information.
Using the Planning Wizard, you can:
Cancel the action and avoid the scheduling conflict.
Microsoft Project will not change the task, and there will be no scheduling conflict.
Continue the action and allow the scheduling conflict.
Project will change the task, and a scheduling conflict will occur. Project will not be able to adjust the task's dates to reflect changes in the dates of the linked task.
If you don't want the Planning Wizard to display this information again, select the Don't tell me about this again check box.