I faced the same issue at start. Even tried putting ../ in behavior:url() but of no use.
When I checked the path for pie.htc in IE, It shows as: folder/css/css/pie.htc.
we reference LESS file with css/style.less
Then behavior:url(css/pie.htc) for .htc file.
put the style.less & pie.htc in same folder as HTML file. so the references would be “style.less” and “pie.htc”. :)