So, I just opened up AE CS5 and linked the two parameters by an expression with no problem. The pick-whip (spiral thing) showed up. so you might need to restart AE, re-install AE, or if that doesn’t work you might need to do lots of typing… i.e. “thisComp.layer(“Null 1”).effect(“Slider Control”)(“Slider”)” to link the parameters.
Hope this helps