I was getting 404 (Page Not Found) when navigating to our SVC files on our Windows Server 2003/IIS 6 boxes. After doing some research, it was suggested to run the following command:

ServiceModelReg.exe /i

Well, that didn't work for me; same problem – page not found. So I tried resetting the extension mapping manually and fortunately, it worked. Here's how:

Right-click the root "Web Sites" node in IIS Manager (inetmgr.exe)

Click the "Configuration" button under the "Home Directory" tab

Select the ".svc" row under the "Mappings" tab and then remove it with, well, the "Remove" button. Click "OK", "Select All", "OK", "Apply", etc. until everything is applied in IIS.

Finally, re-run ServiceModelReg.exe: