Images missing in ESS Webdynpro error messages

Hi all,

When error or warning messages occur in Web Dynpro applications in our Portal, it does not show the correct images. In stead it shows the familiar red cross of Internet Explorer. How can we solve this? Please see screenshot:

http://tweakers.net/ext/f/oA3f70FP737KctSpPtnmG6Wp/full.jpg

Thanks in advance!

Best regards,

Jan