The spell Dimensional lock has the following description:
You create a shimmering emerald barrier that completely blocks extradimensional travel. Forms of movement barred include astral projection, blink, dimension door, ethereal jaunt, etherealness, gate, maze, plane shift, shadow walk, teleport, and similar spell-like abilities. Once dimensional lock is in place, extradimensional travel into or out of the area is not possible.
A dimensional lock does not interfere with the movement of creatures already in ethereal or astral form when the spell is cast, nor does it block extradimensional perception or attack forms. Also, the spell does not prevent summoned creatures from disappearing at the end of a summoning spell.
It also says:
Spell Resistance yes
When are you supposed to check for spell resistance?
When you are trying to "force" the lock by using an extradimensional way of travel?
When the designated "point in space" is positioned on a creature?
Area 20-ft.-radius emanation centered on a point in space
Some other time?