Error messages are kryptic at best... here are some meanings
Deciphering Error messages in ASP.NET Visual Studio
1. The first error has to do with deployment. If you deploy your application to a Win Server 2000, the default ASP.NET framework version would most likely be 1.1. If you have a VS 2005, you would be running under framework 2.0. Here is the Web.Config error you most likely received.
2. If you open your IIS on your webserver and go to your website, there should be a tab for ASP.NET. Make sure you have the 2.0 Framework selected for this site as shown.