The type 'WebPartTests.Test1' exists in both 'c:\WINDOWS\Microsoft.NET\Framework\v2.0.50727\Temporary ASP.NET Files\...\Weather.DLL' and 'c:\WINDOWS\...\App_Code.ukqokk-6.dll'

I am trying to run a web part on my web page using a class file.

The class file is in the App_Code folder and just inherts from the WebPart class:

namespace WebPartTests
{
    public class Test1 : WebPart
    {

        public Test1() { }

        protected override void Render(HtmlTextWriter writer)
        {
            writer.Write("hello");
            base.Render(writer);
        }

    }
}

This should display on the default.aspx page:

<%@ Register TagPrefix="wp" Namespace="WebPartTests" %>
...

        <asp:WebPartZone ID="WebPartZone1" runat="server">
            <ZoneTemplate>
                <wp:Test1 id="TestPart1" runat="server" Title="Web Part Test" />
            </ZoneTemplate>
        </asp:WebPartZone>

However although it builds ok, when I run it I get the following error:

Compiler Error Message: CS0433: The type 'WebPartTests.Test1' exists in both 'c:\WINDOWS\Microsoft.NET\Framework\v2.0.50727\Temporary ASP.NET Files\root\f40803c9\3af30b4d\App_Code.jfw1hrqs.dll' and 'c:\WINDOWS\Microsoft.NET\Framework\v2.0.50727\Temporary ASP.NET Files\root\f40803c9\3af30b4d\assembly\dl3\851dd24c\87bfe724_f0cac801\Weather.DLL'

I have tried clearing out all the temporary files, and changing the batch property for compilation in the web.config file.

What else can I try?

Note this really is just a default.aspx web page and a Test1.cs class file project - there is very little to it.