I don't know. May be it's just a difference between 2.5.8 and 2.6.0 with your script.
So your possible choices are:
- use SVP with your fast Avisynth. It should work, but will need more memory.
- use SVP with it's own Avisynth: you can place SVP's one in the video player's folder (near .exe file), then SVP will use this version instead of one located in SysWOW64.
And don't forget to remove/rename "avisynth.dll" from SVP\Distr\MT folder or else SVP will overwrite SysWOW64\avisynth.dll on each run.