open m3_import_v0.32_x.ms text editor,
replace block:


-- *******************
--  M3 STRUCTURES
-- ******************* 
struct M3I_SeqData
(
	tag, ablock
)

fn M3I_getSize type flags:0 =
(
	local size
	case type of
	(
		#REF: 
		(
			case flags of
			(
				#MD33: size = 0x08
				#MD34: size = 0x0C
			)
		)
		#MD33: size = 0x14
		#MODL:
		(
			case flags of
			(
				23: size = 0x240
			)
		)
		#SEQS: size = 0x58
		#STC_: size = 0x8C
		#STG_: size = 0x10
		#STS_: size = 0x18
		#BONE: size = 0x9C
		#VERT: size = 0x20
		#U16_: size = 0x02
		#U32_: size = 0x04
		#CHAR: size = 0x01
		#DIV_: size = 0x24
		#REGN: size = 0x1C
		#BAT_: size = 0x0E
		#MSEC: size = 0x48
		#MATM: size = 0x08
		#MAT_: size = 0xD4
		#LAYR: size = 0x160
		#IREF: size = 0x40
	)
	
	return size
)

and add:

-- *********************************
--  USER INTERFACE FUNCTIONS
-- *********************************
-- Global UI Funcs
fn M3I_uiOpenFile ftypes &fname =
(
	local ret = getOpenFileName types:ftypes filename:fname
	if ret != undefined then fname = ret
)

utility m3imp "M3 - Import"
(
	group "Model Filename"
	(
		button bOpenFile "Open..."
		edittext tFileName
	)
	
	group "Settings"
	(
		checkBox chkImportMesh "Import Mesh" checked:(doCreateMesh) tooltip:"Imports Model Geometry"
		checkBox chkImportNorms "Import Vertex Normals" checked:(doVertexNormals)
		checkBox chkImportMats "Import Materials" checked:(doCreateMats) tooltip:"Imports Model Materials"
		checkBox chkImportBndSphere "Import Bounding Sphere" checked:(doCreateBndSphere) tooltip:"Imports Bounding Sphere"
		checkBox chkImportSkin	"Create Skin" checked:(doCreateSkin) enabled:(doCreateBones and doCreateMesh) tooltip:"Deforms mesh through bones"
		checkBox chkImportBones "Import Bones" checked:(doCreateBones) tooltip:"Imports Bones from Model"
		checkBox chkImportAttach "Import Attachments" checked:(doCreateAttachments) tooltip:"Imports Attachments"
		checkBox chkImportPemits "Import Particle Emitters" checked:(doCreatePemits) tooltip:"Imports Particle Emitters"
		checkBox chkAnimateObjects "Animate Objects" checked:(doAnimateObjects) tooltip:"Animate Objects"
		checkBox chkTransformBones "Animate Bones" checked:(doTransformBones) enabled:(doCreateBones) tooltip:"Animates model bones"
		spinner spnFPS "FPS:" range:[1,1000,1000] enabled:(doAnimateObjects) type:#integer
	)
	
	button bImport "Import" height:35 width:100 offset:[0,5]
	button bAbout "About" offset:[0,5]
	
	on m3imp open do
	(
		if (doCreateBones != true) then
		(
			chkImportAttach.checked = false
			chkImportAttach.enabled = false
			chkImportPemits.checked = false
			chkImportPemits.enabled = false
			chkTransformBones.checked = false 	
			chkTransformBones.enabled = false
			chkImportSkin.checked = false
			chkImportSkin.enabled = false
		)
		if (chkAnimateObjects.checked != true) then
		(
			chkTransformBones.enabled = false
			chkTransformBones.checked = false
			spnFPS.enabled = false
		)
		if (doCreateMesh != true) then
		(
			chkImportSkin.checked = false
		)
	)
	on chkImportMesh changed state do
	(
		if (state == on) then
		(
			if (chkImportBones.checked != false) then
			(
				chkImportSkin.checked = true
				chkImportSkin.enabled = true
			)
			chkImportNorms.checked = true
			chkImportNorms.enabled = true
			chkImportMats.checked = true
			chkImportMats.enabled = true
		)
		else
		(
			chkImportNorms.checked = false
			chkImportNorms.enabled = false
			chkImportSkin.checked = false
			chkImportSkin.enabled = false
			chkImportMats.checked = false
			chkImportMats.enabled = false			
		)
	)
	on chkImportBones changed state do
	(
		if (state == on) then
		(
			chkImportAttach.checked = true
			chkImportAttach.enabled = true
			chkImportPemits.checked = true
			chkImportPemits.enabled = true
			chkTransformBones.checked = true
			chkTransformBones.enabled	= true
			if (chkImportMesh.checked != false) then
			(
				chkImportSkin.checked = true
				chkImportSkin.enabled = true
			)
		)
		else
		(
			chkImportAttach.checked = false
			chkImportAttach.enabled = false
			chkImportPemits.checked = false
			chkImportPemits.enabled = false
			chkTransformBones.checked = false 	
			chkTransformBones.enabled = false
			chkImportSkin.checked = false
			chkImportSkin.enabled = false
		)
	)
	on chkAnimateObjects changed state do
	(
		if (state == on) then
		(
			chkTransformBones.enabled = true
			chkTransformBones.checked = true
			spnFPS.enabled = true
		)
		else
		(
			chkTransformBones.enabled = false
			chkTransformBones.checked = false
			spnFPS.enabled = false	
		)
	)
	on bOpenFile pressed do
	(
		M3I_uiOpenFile "M3 model (*.m3)|*.m3|All Files|*.*|" &tFileName.text
	)
	on bImport pressed do
	(
		local fname = tFilename.text
		if doesFileExist(fname) then
		(
			doCreateMesh = chkImportMesh.checked
			doVertexNormals = chkImportNorms.checked
			doCreateSkin = chkImportSkin.checked
			doCreateMats = chkImportMats.checked
			doCreateBndSphere = chkImportBndSphere.checked
			doCreateBones = chkImportBones.checked
			doCreateAttachments = chkImportAttach.checked
			doCreatePemits = chkImportPemits.checked
			doAnimateObjects = chkAnimateObjects.checked
			doTransformBones = chkTransformBones.checked
			M3I_useFPS = spnFPS.value
			try
			(
				M3I_Main(fname)
			)
			catch
			(
				messageBox ("Import failed\n"+getCurrentException()) title:"Import failed"
			)
			
		)
	)
	on bAbout pressed do
	(
		messagebox "M3 Importer v0.31 - 05-03-2011\n\xa9 2010, NiNtoxicated (madyavic@gmail.com)\nVisit www.sc2mapster.com for updates and more information\nHead to the forum for support. Feedback is appreciated!" title:"About"
	)
)

fn M3I_AnimUI =
(
	-- Reset
	if (sc2animUI != undefined) do 
	(
		closeUtility sc2animUI
		openUtility sc2animUI
	)
)

I tested the Avernus Skybox.m3 unfortunately not good.