Did you do what QuEnc said to you? Adding the Line ConvertToYV12() to the end of your Video?
try to open the avs with mediaplayer 6.4, bsplayer, virtualdub etc. install the ffdshow filter, that may help.
ConvertToYV12() is already at the end of script... Oops. I think I was using AviSynth 2.0.8 and not 2.5.? I suspect that will solve my problem.