KeesH - 10:14 am on Mar 4, 2012 (gmt 0)

Gents,
I solved the problem. The issue doesn't really belong here.
I just noticed that the IE9 didn't pickup the CSS file at all.
And because I recently was upgraded to an IIS 7.5 server and I also changed the MIMETYPE settings in my web.config for CSS files. That did the trick:
What went terrible wrong in my web.config is this:
<remove fileExtension=".css" />
<mimeMap fileExtension=".css" mimeType="text/css; charset=UTF-8" />
Just keep it to this:
<remove fileExtension=".css" />
<mimeMap fileExtension=".css" mimeType="text/css" />
So no explicit charset settings here!

Thanks anyhow.

Kees