Here is our setup. A website exposed to the internet on IIS 6 .Net2 with an IIRF filter to rewrite urls to point to a website on an internal server.
The internal server has a .Net 4 website which has a page that uses the .Net 4 chart control. All other pages work fine except this one. For the chart a request is made such as this:
/ChartImg.axd i=chart_0_6.png&g=ad769d09b6b647d6a555ad7df03db209 80 - 188.8.131.52 Mozilla/4.0+(compatible;+MSIE+8.0;+Windows+NT+6.1;+Trident/4.0;+SLCC2;+.NET+CLR+2.0.50727;+.NET+CLR+3.5.30729;+.NET+CLR+3.0.30729;+Media+Center+PC+6.0;+.NET4.0C;+.NET4.0E)
401 1 0
The request never makes it through to the internal server from the server exposed to the internet and a 401 error is returned.
On the internal server the page ChartImg.axd doesn't actually exist and is handled by an httpHandler. This doesn't seem to be the problem though as something on the exposed server seems to handling the request and returning the error.
I've been struggling with this all day now and can't seem to find any way round it.