Receiving an error while viewing SSRS report in asp.net page

I have the following in my ASP.net page:

<asp:Button ID="Button1" runat="server" Text="Button" OnClick="Button1_Click" /><rsweb:ReportViewer ID="ReportViewer1" runat="server"></rsweb:ReportViewer>

Code-behind:

protected void Button1_Click(object sender, EventArgs e)
		{
			ReportViewer1.ProcessingMode = Microsoft.Reporting.WebForms.ProcessingMode.Remote;
			ReportViewer1.ServerReport.ReportServerUrl = new Uri("http://wserv/ReportServer/");
			ReportViewer1.ServerReport.ReportPath = "/IR/Checklists";
			ReportViewer1.ServerReport.Refresh();
		}

I get the following error:

Unhandled exception at line 751, column 5 in

https://localhost:00003/Pages/MyPage.aspx

0x800a1391 - Microsoft JScript runtime error: 'Microsoft' is undefined

What is causing the error and how do I fix it?