Check if you set the ReportSource correctly - How to: Set ReportSource for Report Viewers
. Also, make sure Telerik.Reporting.dll
assemblies physically exist in the bin folder of your application - Deploying Web Site
Note that WebSite projects have to be configured manually due to their specific handling of references. In a web application, dragging the viewer on the design surface will work as expected.
Regarding you last question, in VS Designer, you can set the parameters from Edit Parameters dialog when you specify the ReportSource for the viewer. Another option is to set parameters programmatically - please see an example in How to: Set ReportSource for Report Viewers
/Set the Report Source programmatically help article.
Please note, that ASP.NET Web Forms Report Viewer
is a legacy report viewer and for new projects our recommendation is to use the latest web forms report viewer - HTML5 Web Forms Report Viewer
In case, this information does not help please open a support ticket and attach the problematic project so we can test it locally.
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