I had some really frustrating hours with the new version of the Reporting Services Report Web Viewer today. We are using local reports, which we actually create dynamically (subject of another post), but we couldn’t get them to be showed by the Report Web Viewer. We started to seek the problem way off, because we of course assumed that the problem had to do with our creating of the report. Finally we took a step back and tried to get some really simple things to work, but with the same problem. The behavior was that the report viewer continuisly kept refreshing/posting for the report but never displaying it. After some searching I found this blog “Reports Never Stop Loading With VS 2010” and it turns out that the behavior of v9/VS2008 and v10/VS2010 is totally changed. The new version doesn’t use frames and HTTP handler anymore, but instead uses the AJAX support in ASP.NET. This means that the request for the report returns to the aspx page hosting the report viewer, but we did not check for IsPostback before initializing the viewer with the report and data which made us restart the process over and over again. Read the blog post above for details.