I still get that same error even now when I am using the optimal script v4 and I have AviSynth 2.5.4 installed.
This is my script:
Code:
AviSource("D:\My Films\ss.avi",false)
SwapUV()
BlindPP(cpu=4)
Blockbuster(method="noise",detail_min=1,detail_max=3,variance=0.1,seed=1)
Convolution3D(1, 6, 12, 6, 8, 2.8, 0)
GripCrop(544, 480, overscan=1, source_anamorphic=false)
GripSize(resizer="LanczosResize")
Undot()
TemporalSoften(2,7,7,3,2)
DCTFilter(1,1,1,1,1,1,0.5,0)
#Blockbuster(method="noise",detail_min=1,detail_max=10,variance=0.3,seed=5623)
TextSub("D:\My Films\ss.srt")
GripBorders()
EDIT:
I've fixed the problem

, AviSynth/VirtualDub script reader v0.1 was unticked in Enviromental settings.