Oh, so I copied DGdecode.dll to MeGUI's directory and successfully created an avs!
But the error loading the AVS is still the same. I'm not sure about the YV12 decoder you asked me. Graphedit only shows 3 boxes. The avs one, linked to ffdshow MPEG-4 Video Decoder then linked to VMR Video Renderer.
Well, ffdshow wan't supposed to be there, am I right? I use it because I check "Uncompressed" on ffdshow Codecs options. I like ffdshow's processing so I use it with all videos.
I'll disable ffdshow and see what happens. Thanks a lot for your help Doom.