The barebone example centers the thumbstrip -
http://www.highslide.com/examples/galle ... strip.html
Your page gives a javascript error in IE caused by adding the blockRightClick above the call for the highslide js file, but this isnÔÇÖt causing the missing centering.
The missing centering is caused by the setting for width for .highslide-thumbstrip-horizontal div. You have 100% - it should be auto. You probably didnÔÇÖt upgrade your css file when upgrading Highslide.
.highslide-thumbstrip-horizontal div {
width: auto;
}