Getting "Unknown error occurred" from ffmpeg with .avs input

[Starduster]

I have an .avs that combines .mp3 with .jpg's and it plays fine in Windows media player. Its contents are:

VD = DirectShowSource("slide1.mp3", audio=True)
VD = getChannel(VD,1,1)
VD = ssrc(VD, 44100)
FV=ImageSource("slide1.jpg",fps=15,start=1,end=ceil(15*AudioLengthF(vd)/AudioRate(vd))).ConvertToRGB32().Lanczos4Resize(800,600)
sld1 = AudioDub(FV, VD)
VD = DirectShowSource("slide2.mp3", audio=True)
VD = getChannel(VD,1,1)
VD = ssrc(VD, 44100)
FV=ImageSource("slide2.jpg",fps=15,start=1,end=ceil(15*AudioLengthF(vd)/AudioRate(vd))).ConvertToRGB32().Lanczos4Resize(800,600)
sld2 = AudioDub(FV, VD)
sld1 ++ sld2

I'm using 2.6.0 and the latest version of ffmpeg (ffmpeg-20160409-git-0c90b2e-win64-static) to create an .flv using:

ffmpeg -i 223_0_0.avs 223_0_0.flv

When I run ffmpeg, I get "Unknown error occurred". I've used AVIsynth for years but this is the first time I've tried to use an .mp3 as audio. Do I need anything else in the script file or does anyone know what I'm doing wrong?

[Starduster]

I installed a new 64 bit version of fffmpeg and the 64+ version of AVIsynth and all is working again.