openInfoWindowHTML not working on GMarker array

Hi folks. I've been reading through some posts and guides but cannot
figure out why I'm getting an error. Specifically, Mike Williams'
guide has been a great help:

http://www.econym.demon.co.uk/googlemaps/basic2.htm

I've got a map I'm loading with the onload function because it won't
work in IE otherwise. My problem occurs when I try to pop up the info
window from an html 'sidebar' (actually below the map) within the page.

I globally declare arrays of points, html segments and markers, so the
linkClick function (called when they click a link) is able to see them,
and it can read and act on the point and html segment arrays. However,
it keeps giving me the "Object doesn't support this property or
method." error in IE on the line that references the marker array:

mapmarkers[i].openInfoWindowHTML(maphtmls[i]);

I can't figure out where my mistake is and it's driving me nuts. I'm
declaring it and filling it the same way I'm filling the html array,
but it still won't behave. I've got my onload function named properly
(executemap()), and the linkClick() function is executing otherwise
(centers on the corresponding point[] array item).

You can see my page here:

http://colemanpropertiesinc.com/map.html

and the error it is throwing is on line 43.

I'm no javascript guru but I know a little bit, so I'd like to hope
it's not a syntax mistake.

Any help would be appreciated. Thanks!