wix installer schema not found

I am new with Wix installer. I am having problem with building the set-up project.

It says;

The Bundle element contains an unexpected child element 'util:RegistrySearch'

I have already referenced the dll into the project and have;

<?xml version="1.0" encoding="UTF-8"?>
<Wix xmlns="http://schemas.microsoft.com/wix/2006/wi" 
     xmlns:util="http://schemas.microsoft.com/wix/UtilExtension">

in the bundle.wxs

When I go to the link below; http://schemas.microsoft.com/wix/UtilExtension

I have the error ;

The resource you are looking for has been removed, had its name changed, or is temporarily unavailable

However; when I comment out the .UtilExtension and util:RegistrySearch, the project builds and works well. I think it should not build if it is a schema problem because;

<Wix xmlns="http://schemas.microsoft.com/wix/2006/wi" 

stays still there.