My blog and all the sites in and around it are a mix of .NET 2.0, 3.5 and 4. This blog engine is currently .NET 3.5 and runs at http://hanselman.com/blog , but the application at http://hanselman.com/ (the root) is .NET 4. You can happily mix and match applications across .NET versions on a single IIS instance. You can see how mixed my system is in the screenshot at right there. However, things got messy when I changed the parent / application to .NET 4, but kept the child /blog as .NET 3.5 (the 2.0 CLR). I got lots of errors like Unrecognized attribute 'targetFramework'. Note that attribute names are case-sensitive. The targetFramework attribute was inherited from the root .NET 4 Web.config file in the Default Web Site root using ASP.NET configuration...(read more)
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