I Have This Problem When Loading The AVS File
This is not a problem of MeGUI as MeGUI itself does not require this file.
I had more or less the same problem a few weeks ago. Reason for me was the file SSE2tools.dll in the AviSynth\Plugins folder (not the MeGUI one - the general Avisynth fodler). I copied the file msvcr71.dll into that folder and the problem was gone. msvr71.dll should be located in one of your folders below c:\windows (search for it).
I suggest that you use Process Monitor and Dependy Walker to find out which file is causing the problem.