I’ve had a problem with one of my sites, in which IE8 had a javascript error and I needed to use IE7 rendering mode, which was ok.

I this case I found two solutions:

1. Meta tag solution :

<meta http-equiv="X-UA-Compatible" content="IE=EmulateIE7">

2. htaccess file solution

Header set X-UA-Compatible IE=EmulateIE7

In my case the .htaccess file version worked just fine