Maybe check that you also have in SysWOW64, fftw3.dll, and libfftw3f-3.dll, x86.
And in system32, same files for x64.
EDIT: Also, its a bit daft having to have some reasonably complex script in plugins, just to have access to eg IsAvsPlus(),
better to add some always present *.avsi script for such things, containing eg.
AvsInit.avsi
Code:
Function IsAvsNeo() { FindStr(VersionString, " Neo") != 0 }
Function IsAvsPlus() { FindStr(VersionString, "AviSynth+") != 0 || IsAvsNeo }
Function AvsPlusVersionNumber() { IsAvsNeo ? eval(MidStr(VersionString(),20,4)) : IsAvsPlus ? val(MidStr(VersionString(),17,4)) : 0 }
Function IsAvs26() { VersionNumber >= 2.6 }
# SetMemoryMax(1024) # Or whatever.
If above installed in plugs, then having same functions in some other script as well, will not matter.