You could try built in python methods to get mxds instead of your own logic
import arcpy, os
fileFolder = r"G:\ProjectF\GIS\Projects\INRMP\Burlington\GIS_Maps\\"
dirs = os.listdir(fileFolder)
maps = [(fileFolder + dir) for dir in dirs if dir.endswith(".mxd")]
oldSpace = r"G:\ProjectF\GIS\Projects\INRMP\Burlington\GIS_Data\Burlington GIS\ANG_Burlington\ANG_Burlington_CIP.mdb\cadastre\installation_area"
newSpace = r"G:\ProjectF\GIS\Projects\INRMP\Burlington\GIS_Data\Burlington GIS\VTANG_Boundary.shp"
for map in maps:
mxd = arcpy.mapping.MapDocument(map)
mxd.replaceWorkspaces(oldSpace,"ACCESS_WORKSPACE",newSpace,"SHAPEFILE_WORKSPACE")
mxd.save()
del mxd