php and javascript error

I've just run into this problem this morning.... <a href="#" onclick="javascript:window.open('web_forward.php?address=<? echo $web_url; ?>&agent=<? echo $agent; ?>&real_company_name=<? echo $real_company_name; ?>', 'Web Site');"> This produces an "Error on Page" in IE 7, but works perfectly in Firefox and Netscape. I have several other javascript calls on the page where this call resides and all of them work perfectly except for this one. Does this error occur because I'm sending the variables to another script that does some logging then forwards the user to the URL or is it just a IE quirk?