ASP dynamically created image, unable to display in web browser control-Collection of common programming errors

I’m currently under the belief it may be to do with the header information but I’m really not too sure. The image on this page is the best example of it that I can give. It will display sometimes in a web browser control, and other times it just plain refuses to. Does anyone have any idea as to why?

The code I’m using to try and grab the image is simply:

WebBrowser.Navigate("http://www.lse.co.uk/tools/user/imgChatUsagePie.asp?nick=mulledwine", null, null, "image/gif");

It’s really hard to ascertain as to what is causing the image to display sometimes and others not as it works completely fine within Chrome. Is this a problem related specifically to the web browser control?

Thank you in advance.