c# - Encryption web.config file "aspnet_regiis.exe" not working -

i work asp.net fromwork 4.0 web site. , want encrypt web.config file connectionstring. used aspnet_regiis -pef "connectionstring" "file location"

but it's not working. rather i'm getting error message shown below

<?xml version="1.0"?> <!--   more information on how configure asp.net application, please visit   http://go.microsoft.com/fwlink/?linkid=169433   --> <configuration>     <system.web>     <compilation debug="true" targetframework="4.0"/>     <httpruntime/>   </system.web>    <connectionstrings>         <add name="ms_eas_locationconnectionstring" connectionstring="data source=help\sqlexpress;initial catalog=ms.eas.location;user id=sa;password=123" providername="system.data.sqlclient"/>   </connectionstrings>  </configuration>