error when adding anchor point expression..... disabled

I'm trying to create a quick/sudden shake during an impact in AE CC to a comp inside of the master comp.

Like a big object impacting a wall, i want the entire project to shake for a split second at impact.

created null and added to slider effects to it

the error message displays when i alt/click anchor point and enter this command: wiggle(0,0)

i get this error: Error at line 1 in property "anchor point" of layer 2 in (mycomposition) in comp 'Comp 1'. , does not have a value.

what am i doing wrong?