I also am having a problem with the ReportViewer not working after having moved my project into VS2010 and .NET 4.0.  The ReportViewer shows no data for my drop down controls and no chart.  I have added the <handler> to web.config that I found in another post:
    
I am currently running Telerik Reporting Q3 2008 SP2 (v2.9.9.202). Would updating to a newer version help?
Thanks. Dan
                                | <system.webServer> | 
| <handlers> | 
| <add name="Telerik.ReportViewer.axd_*" path="Telerik.ReportViewer.axd" verb="*" type="Telerik.ReportViewer.WebForms.HttpHandler, Telerik.ReportViewer.WebForms, Version=4.0.10.317, Culture=neutral, PublicKeyToken=a9d7983dfcc261be" preCondition="integratedMode,runtimeVersionv4.0" /> | 
| </handlers> | 
| <validation validateIntegratedModeConfiguration="false" /> | 
| </system.webServer> | 
I am currently running Telerik Reporting Q3 2008 SP2 (v2.9.9.202). Would updating to a newer version help?
Thanks. Dan

