I've depoyed a site live and found I needed to include some custom styling for browser compatibility and included a .htc file in my app_themes/ThemeName/ directory. The site functions as expected and I see the newly changed design in different browsers. But the minute I go to the CMSDesk to edit or design mode I get page cannot be displayed and an error log of:

PageNotFound
Event URL: /cms/App_Themes/ThemeName/PIE.htc
URL Referrer: http://www.SiteName.com/CMSModules/Content/CMSDesk/Edit/editpage.aspx?nodeid=2&mode=design

Here is the reference I have in my CSS sheet: behavior: url(../App_Themes/ThemeName/PIE.htc); The minute I remove the behaviour reference, the site works as expected.