Quick Fix 1

Reopen visual studio in administrator mode. (Right click on the visual studio icon and click on 'Run as Administrator'). 

Quick Fix 2

Start->Programs->Accessories-> Command Prompt (Rt Click)->Run as Administrator (For Win 8 Windows Key-> type cmd-> Run as Administrator)
On the Cmd Prompt Type: netsh http add urlacl http://+:8000/ user=DOMAIN\UserName

Details

While running WCF services in Windows Vista or greater you may encounter a namespace reservation exception. This occurs because windows account starting from vista does not grant administrative privileges to user accounts (even if your account has administrative privileges). Your service does not have the permissions to use the address you have specified for your endpoint. You may get the following exception while running your service:

HTTP could not register URL http://+:8000/. Your process does not have access rights to this namespace (see http://go.microsoft.com/fwlink/?LinkId=70353 for details)

In order to resolve this issue you need to provide the account under which your service is running the permissions to use the address specified for the endpoint.

Run Command Prompt under elevated mode (Start->Programs->Accessories->Command Prompt (Rt Click)->Run as Administrator). On the command prompt type the following:

netsh http add urlacl http://+:8000/ user=DOMAIN\UserName