I looked at your website and saw a number of isues which could be causing the popup to not display properly. Most of theme are theme related.
- the line <meta http-equiv="X-UA-Compatible" content="IE=EmulateIE7"/>
This line basicly forces internet explorer to render the page as internet explorer 7 (even if you are using a higher version.
- The doctype is improperly specified (could be caused by minimization):
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
with something from: http://www.w3schools.com/tags/tag_doctype.asp
(linebreaks are important to keep with doctypes).
I think fixing the doctype and removing the emulate line should work since the ligtbox requires IE8+ and a valid doctype.
You can make the required change by editing header.php via ftp or the build-in theme editor