After building, a WCF service in Windows Server 2003, I thought no big deal, for Windows Server 2008.  I deployed the service on my Windows Server 2008 machine and started getting 404.3 errors only with my WCF service.  After checking that I had all of the necessary dependencies:

• 3.0 Framework
• WCF Activation installed
  • This can be found under  the 3.0 framework options. Depending on your operating system this could be under different locations. 
    • Vista  : Control Panel -> Program and Features -> Turn on/ off Windows Features -> Microsoft.NET Framework 3.0
    • Server 2008 : Server Manager -> Add Features-> .Net Framework 3.0 Features -> WCF Activation

I kept getting 404.3 errors, so I started examining IIS to make sure that the right stuff is registered.  After not finding anything wrong, I started looking at the WCF installation. I found that my WCF services where not installed.  You can do the installation manually by running "ServiceModelReg.exe", which was found at %Windows%\Microsoft.Net\Framework\v3.0\Windows Communication Foundation\.

To check status run:
Command: ServiceModelReg -vi
Result: The expected result if "Default Installation" next to the features shown, otherwise the services are not active. 

To turn on Services:
Command: ServiceModelReg -i
Result: Installation of WCF services in IIS 7(6)

I was then able to immediately test my service and see that I could get to the WSDL.

Hopefully this fixes your 404.3 issue.

David Waddleton