The Report Viewer installs the Crystal Reports runtime to run reports. It is reported that if you install another report viewer, from another company, it will install another Crystal Reports runtime package. This may be an older, out-of-date, install, or one that is not compatible with the Report Viewer from ReportViewer.biz. When you then try to run a report with The Report Viewer, the report may not load, giving an error message that says, "Report failed to load."
Uninstalling the competing software and reinstalling The Report Viewer from Report Viewer Limited should solve this issue.