Parser Error - help

I get this whenever i run my solution.
What's the cause of this.
thanks

Description: An error occurred during the parsing of a resource required to service this request. Please review the following specific parse error details and modify your source file appropriately.

Parser Error Message: 'URSL.RS7a' is not a valid base class because it does not extend class 'System.Web.UI.UserControl'.

Source Error:


Line 1: <%@ Control Language="vb" AutoEventWireup="false" Codebehind="RS7a.ascx.vb" Inherits="URSL.RS7a" TargetSchema="http://schemas.microsoft.com/intellisense/ie5" %>
Line 2: <table style="FONT-WEIGHT: bold; COLOR: mediumblue">
Line 3: <TR>


Source File: c:\inetpub\wwwroot\URSL\UserControls\RS7a.ascx Line: 1