Unrecognized attribute 'xmlns'.

this error actually means that the site is running old Framework version,
what you need to do is the following:
1.Open Internet Information Services and navigate to "Default Web Site" (or the site you're using as your default).
2.Right click the Site icon (the one with the globe).
3.Select the ASP.NET tab. You'll see a drop-down with the available versions (if you're getting the error, odds are, you'll see 1.1).
4.Select the proper build of ASP.NET 2.0 (or later, depends on the version you worked on in the developing stage).
5.Restart IIS.