does directshow work for you ?
render the file in graphstudio, what does it say? is it the microsoft decoder ? if it is, avisynth won't work for you configured like that. Use the win7dsfiltertweaker suggested above to change h264 decoder to ffdshow, then try your program again
if that doesn't work , you can try avisynth virtual file system to mount a "dummy avi"
http://forum.doom9.org/showthread.php?t=133313