The Lock elements button enables you to freeze all elements on the page. When elements are locked you will be no longer able to use the mouse to move, resize or rotate elements.
An elements size, position and rotation can still be changed by opening the settings dialog box of each element in the Position tab, common to all elements.
Activating the lock element option will cause the lock icon on the status bar to be displayed. You will be able to unlock the elements by clicking the status bar as well.
The lock elements command is completely independent from the Enable mouse action option found under the Position tab of the Settings forms. In fact, when then Lock elements is active, it is still possible to double click on each element to enter the Settings dialog box (as long as the Enable mouse action was not disabled for that element).