wpf - isEnabled binded to other button click -

i can't figure out resource missing work, getting messages ei namespace not found.

        <button           name="btnenter"         click="btnenter_click"         style="{staticresource signbuttons}"         fontfamily="comic"         fontsize="24"         fontweight="demibold"         grid.column="3"          height="51.562"         width="75"         margin="30,23.624,0,0"         grid.row="3"         template="{dynamicresource enterbutton}">             <i:interaction.triggers>                 <i:eventtrigger eventname="click">                     <ei:changepropertyaction                      targetobject="{binding elementname=btnmultiplication}"                      propertyname="isenabled" value="false"/>                 </i:eventtrigger>             </i:interaction.triggers>         </button> 

here namespaces

<window x:class="button_template.mainwindow"     xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"     xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"     xmlns:d="http://schemas.microsoft.com/expression/blend/2008"     xmlns:local="clr-namespace:button_template"     xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"     xmlns:i="http://schemas.microsoft.com/netfx/2009/xaml/presentation"      mc:ignorable="d" 

i suggest follow these steps when adding changepropertyaction, callmethodaction, etc... 1. go blend , open project, , select control want insert changepropertyaction

after add changepropertyaction blend automaticly add xmlns extensions.

so won't have manualy. after save in blend, go vs , reaload project , continue.

important interaction added on selected control in objects , timeline window.