Flash CS3 Tutorial
How to Lock Flash Layer Content
Once you've arranged the layer content, it is important that the objects aren't accidentally moved.
By locking the layer, the layer objects cannot be selected or modified. It also prevents you from adding any unwanted objects to the locked layer.
Make sure the timeline/layers panel is open by choosing Window > Timeline.
Add a rectangular object to the workspace with the Rectangle tool (r key).
Click the layer dot below the lock icon to lock the layer.
Choose the Selection tool (v key) and attempt to re-position the rectangle. Nothing happens because the layer is locked.