Action causes a 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 the task. When a task is linked, the predecessor task's start or finish date drives the successor task's start or finish date. If the successor task is also constrained to a fixed date and this date conflicts with the dates driven by the predecessor, the task dependency cannot be honored because the linked task cannot drive the successor's start or finish. You can avoid this scheduling conflict by canceling this action with the Planning Wizard.
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 linked task's dates.
If you don't want the Planning Wizard to display this information again, select the Don't tell me about this again check box.