In IIS 7, we need to make sure we configurate the ReportViewer handler.
You can follow these steps:
o Open Internet Information Services (IIS) Manager and select your Web application.
o Under IIS area, double-click on Handler Mappings icon.
o At the Action pane on your right, click on Add Managed Handler.
o At the Add Managed Handler dialog, enter the following:
Request path: Reserved.ReportViewerWebControl.axd
Type: Microsoft.Reporting.WebForms.HttpHandler
Name: Reserved-ReportViewerWebControl-axd
o Click OK.
http://forums.asp.net/t/1361939.aspx
For more information, see http://otkfounder.blogspot.com/2007/11/solving-reportviewer-rendering-issue-on.html
