Here is how to innitialize a post process shader from a script.
:state=20,framebeyond=2 15,plrdistwithin=150:
setposteffect=refract,plraddhealth=-10,sound=audiobank\misc\melee.wav,state=23
:state=20:incframe=2,rotatetoplr
:state=20,frameatend=2:
setposteffect=none,state=4
:state=23:incframe=2
:state=23,frameatend=2:setposteffect=none,state=4
Notice the items in Bold.
You must have post process set to 1 in the setup.ini file. All postscript shaders should be in the effectbank\postprocess folder.
Post which ai script you are using and I will guide you thru it.