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The install directory for a given Maya version is determined by looking at the registry key HKEY_LOCAL_MACHINE\SOFTWARE\Autodesk\Maya\VERSION\Setup\InstallPath (64-bit or native 32-bit) or HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Autodesk\Maya\VERSION\Setup\InstallPath (32-bit Maya on 64-bit Windows). These keys are set by the Maya installer. If you ever move Maya to a different directory after installing it, make sure you update the corresponding keys, or the Maxwell plug-in installer will be unable to find the new path.
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