There are no known problems with IE9. We test here with it and have many, many users who have not reported any problems in this area – and that is a very popular plugin.

It suggests – not conclusively of course but likely – that this is going to come down to something in your site environment. Note that what you are seeing there is NOT a blank page. it is a 404 page meaning that IE failed to find the page it was supposed to load. We know it is there of course, as other browsers load it fine.

So the question really is what is different about using IE on your site? It might be another WP plugin that performs something ‘special’ if the browser is IE? This could be a hangover from the older IE6/7 days when you needed to provide special hacks for some stuff to work in IE that is no longer necessary.

It could just be the browser cache is at fault. IE8 and IE9 do a horrible job on trying to cache more than they should so try emptying it. It might also be a server-side setup that is doing something if it detects IE in use. That is something you would need to ask your host. In particular ask them if they have mod_security installed and could that cause a 404 on a good url when IE was used.