IE can't open a new window.

One of the blokes at work called me over with a problem where clicking on a link in IE with a target="_blank" didn't open a new window in his webpage he was developing. The browser seemed to redraw itself/flicker (the *whole* browser as opposed to the web page content) but nothing else happened. Then Microsoft support article 281679 points to a article a href="http://support.microsoft.com/kb/281679/EN-US/">You cannot open a new Internet Explorer window or nothing occurs after you click a link. I followed the instructions and it all started working again after reregistering shdocvw.dll. No idea why this had failed to work in the first place, but he was using our customised version of ie, which claims can be the culprit. However it works ok on other machines on our network.