Cannot open mp4 file

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I've installed XP64 on my new computer and something went horribly wrong. WMP does not play mp4 files which means DirectShow does not play mp4 files. MPCHC plays them fine, but this is not my goal. My goal is to open them in AviSynth.

Original situation

AviSynth DirectShowSource: Could not open as video or audio.
Video returned: "DirectShowSource: couldn't open file xxx: Cannot play back the file. The format is not supported."

AviSynth DSS2: "Can't open xxx: 80040154"

Insurgent test render: "Unsupported Stream! (VFW_E_UNSUPPORTED_STREAM)"

GraphEdit render: "Cannot play back the file. The format is not supported. (Return code: 0x80040265)

After Haali is installed with mp4 support

AviSynth DirectShowSource: "The specified module could not be found"

AviSynth DSS2: "Can't open xxx: 80040217"

Insurgent test render: "DirectShow Error: 0x8007007e: The specified module could not be found."

GraphEdit render: "The specified module could not be found. (Return code: 0x8007007e)

HALP!

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Sorry about the fuss. Turns out, it wanted a 32-bit video decoder and I've installed ffdshow 64-bit. With regular ffdshow everything works fine. Thought, I'd let you know.