Maybe too late now, but more often than not you need to run
aspnet_regiis.exe -i
after installing asp.net. Maybe I would do it anyway now.
In addition to above, if you need WCF support, you might need to run this:
c:\Windows\Microsoft.NET\Framework\v3.0\Windows Communication Foundation\ServiceModelReg.exe -i
Replace v3.0 to whatever your current framework version is.
I encountered this error from IIS 8.5 when trying to access a WCF service I had written. Turns out the server didn't have the WCF HTTP Activation features turned on. Checked the boxes and clicked through the wizard, iisreset, started working.
