properties - The 'Content' property is set multiple times -

i have created grid type uniformgrid, data : binding (a list of class sql)

my list scrollable, it's great.

but, need add fixed button in top , fixed label on bottom, when scroll want see button , label.

i have error : 'content' property set multiple times.

my code xaml :

<window     xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"     xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"     xmlns:local="clr-namespace:plutus" xmlns:d="http://schemas.microsoft.com/expression/blend/2008" xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" mc:ignorable="d" x:class="plutus.mainwindow"     title="mainwindow" height="523.725" width="898" background="#ff3a3939" windowstartuplocation="centerscreen" windowstate="maximized"> <window.resources>     <style targettype="scrollbar">         <setter property="width" value="35"/>     </style> </window.resources>  <button></button>  <scrollviewer verticalscrollbarvisibility="auto" >     <itemscontrol x:name="lvdatabinding" horizontalcontentalignment="stretch" borderthickness="0" margin="10" grid.row="3" background="{x:null}" itemssource="{binding}" foreground="white">         <itemscontrol.itemtemplate>             <datatemplate datatype="{x:type local:cl_operation}">                 <border borderbrush="white" borderthickness="1" cornerradius="3" margin="0,3" grid.columnspan="0" background="transparent" horizontalalignment="left" verticalalignment="top">                     <grid width="{binding strwidth}" height="60" background="transparent" margin="0,1">                         <grid.columndefinitions>                             <columndefinition width="0.08*" />                             <columndefinition width="0.1*" />                             <columndefinition width="0.1*" />                             <columndefinition width="0.2*" />                             <columndefinition width="0.1*" />                             <columndefinition width="0.2*" />                             <columndefinition width="0.1*" />                             <columndefinition width="0.2*" />                         </grid.columndefinitions>                         <grid.rowdefinitions>                             <rowdefinition />                             <rowdefinition />                             <rowdefinition />                         </grid.rowdefinitions>                         <uniformgrid  grid.column="0" grid.row="0" grid.rowspan="3" background="#ffff8200">                             <textblock text="{binding strpriorite}" fontsize="36" foreground="red" horizontalalignment="left" verticalalignment="center" fontweight="bold" />                             <textblock text="{binding strsssect}" fontsize="12" foreground="black"  horizontalalignment="center" verticalalignment="bottom" fontweight="bold" />                         </uniformgrid>                         <uniformgrid  grid.column="1" grid.row="0" grid.rowspan="3">                             <textblock text="{binding strretardavancetext}" fontsize="28" foreground="{binding scbcolorretardavance}" fontweight="bold" horizontalalignment="center" verticalalignment="center" />                         </uniformgrid>                         <uniformgrid grid.column="2" grid.row="0" grid.columnspan="2" grid.rowspan="2">                             <uniformgrid.style>                                 <style targettype="{x:type uniformgrid}">                                     <style.triggers>                                         <trigger property="ismouseover" value="true">                                             <setter property="background" value="gray"/>                                         </trigger>                                     </style.triggers>                                 </style>                             </uniformgrid.style>                             <textblock text="{binding strnoofop}" fontsize="28" foreground="white" fontweight="bold" mouseleftbuttonup="test"/>                         </uniformgrid>                         <uniformgrid  grid.column="2" grid.row="2" grid.columnspan="3">                             <textblock text="{binding strdescriptionop}" fontsize="14" foreground="white"/>                         </uniformgrid>                         <uniformgrid grid.column="4" grid.row="0">                             <textblock text="{binding strnoarticle}" fontsize="14" foreground="white"/>                         </uniformgrid>                         <uniformgrid  grid.column="4" grid.row="1">                             <textblock text="{binding strdateformatee}" fontsize="14" foreground="white"/>                         </uniformgrid>                         <uniformgrid grid.column="5" grid.row="0">                             <textblock text="{binding strpcesposte}" fontsize="14" foreground="white"/>                         </uniformgrid>                         <uniformgrid  grid.column="5" grid.row="1">                             <textblock text="{binding strtpsposte}" fontsize="14" foreground="white"/>                         </uniformgrid>                         <uniformgrid  grid.column="6" grid.row="0">                             <textblock text="{binding strtempsposte}" fontsize="14" foreground="white"/>                         </uniformgrid>                         <uniformgrid  grid.column="6" grid.row="1">                             <textblock text="{binding strclient}" fontsize="14" foreground="white"/>                         </uniformgrid>                         <uniformgrid  grid.column="6" grid.row="2" grid.columnspan="2">                             <textblock text="{binding strtypeop}" fontsize="14" foreground="white"/>                         </uniformgrid>                     </grid>                 </border>             </datatemplate>         </itemscontrol.itemtemplate>         <itemscontrol.itemspanel>             <itemspaneltemplate>                 <uniformgrid columns="2"/>             </itemspaneltemplate>         </itemscontrol.itemspanel>     </itemscontrol> </scrollviewer> 

thank help.