There should be no script attached to that wall for it to be invisible.
The script in the Easter Pack only contain this statement.
function invisible_wall_init(e)
end
function invisible_wall_main(e)
Hide(e)
end
You can copy it from here and see if it makes a difference.
Intel(R) Core(TM)2 Quad CPU Q6600 @ 2.40GHz, 2400 Mhz, 4 Core(s), 4 Logical Processor(s), 8gb RAM, Nvidia gtx660, Windows 7 Pro 64bit, Screen resolution 1680 x 1050.