You've configured reporting with TMG, and you've published the generated reports content on an IIS 7.5 Server (Windows 2008 R2) so that TMG administrators in your organization can access these reports from their workstation using a standard browser like Internet Explorer.
Problem: The Reports aren't displayed correctly in the browser. You notice that images are missing, hence the "red cross" error as we can see in the below screenshot.
The screenshots below summarized the steps to be done in IIS:
As a result, IIS will respond to such requests (without file extension) with 200 OK with a MIME type of application/octet-stream. Then the client browser will manage how to render the response.
In this case, IE detects that it's an image and will render it as such.
Note: It's recommend hosting the reports inside a dedicated virtual directory and adding the above mentioned setting at this virtual directory level.