Google api markers not appearing in IE8

I have a map at the following address:

It seems to work fine in IE9, Opera, Safari, Firefox but in IE8 it gives me the following message:

‘markers[…].type’ is null or not an object

the code looks like the following

// create arrays of markers of the various types
for (i = 0, len = markers.length; i < len; i++) {
markerGroups[markers[i].type].push(createMarker(markers[i]));
}

I just don’t understand why it will not work in IE8

any help would be appreciated

thanks