Running WCF 3.5 app under .NET 4.0 website -

I have a website hosted on IIS 6 and set to use Net 4.0, but I still have Also WCF service is using Site 3.5 when I browse my SVC file, I get an error:

  unrecognized attribute 'targetFramework'  

More websites on the web web I have tried this and still get the same error. My site is using a different app pool than my WCF service, and the properties are configured to use 4.0 in the ASP.NET tab. I have also checked and I am convinced that my WCF service is using 3.5 (2.0) in my ASP.NET property tab.

IIS6 does not compile versions of composite structures if you can switch to iis7 or Both projects have the same Version that can solve the problem