I did try to run the script a few times and updated script like you posted above. But I always have the same issue: The encoder shuts down every time I hit the "encode" button.
I also tried exactly the script you have posted (for NTSC-source) and have the same problem. I assume, that one of my avisynth-dll's is the wrong one, but I'm not sure which one it is. I did download RemoveGrain and RemoveDirt from your link above but it didn't help.
So could you maybe post the download links of the .dll's you've been using or maybe make a zip-file of your .dll' and load them up to rapidshare? This would help...