I am getting the following error
"ConfigurationErrorsException was unhandled,   Configuration system failed
to initialize"

This were working fine in Web based application and i am porting it to
windows form, the only thing that i removed is the version ifnormation for
the type in namevalue

I am using Windows Form & .net 2.0

Here is the App.config
===================================================
<?xml version="1.0" encoding="utf-8" ?>
<configuration>
   <system.diagnostics>
       <sources>
           <!-- This section defines the logging configuration for
My.Application.Log -->
           <source name="DefaultSource" switchName="DefaultSwitch">
               <listeners>
                   <add name="FileLog"/>
                   <!-- Uncomment the below section to write to the
Application Event Log -->
                   <!--<add name="EventLog"/>-->
               </listeners>
           </source>
       </sources>
       <switches>
           <add name="DefaultSwitch" value="Information" />
       </switches>
       <sharedListeners>
           <add name="FileLog"
                type="Microsoft.VisualBasic.Logging.FileLogTraceListener,
Microsoft.VisualBasic, Version=8.0.0.0, Culture=neutral,
PublicKeyToken=b03f5f7f11d50a3a, processorArchitecture=MSIL"
                initializeData="FileLogWriter"/>
           <!-- Uncomment the below section and replace APPLICATION_NAME
with the name of your application to write to the Application Event Log -->
           <!--<add name="EventLog"
type="System.Diagnostics.EventLogTraceListener"
initializeData="APPLICATION_NAME"/> -->
       </sharedListeners>
   </system.diagnostics>

 <configSections>
   <sectionGroup name="CUSTOMSECTION">
     <section  name="DEV"
type="System.Configuration.NameValueSectionHandler,System"
restartOnExternalChanges ="false" />
     <section name="TEST"
type="System.Configuration.NameValueSectionHandler,System"
restartOnExternalChanges ="false"/>
     <section name="PROD"
type="System.Configuration.NameValueSectionHandler,System"
restartOnExternalChanges ="false"/>
   </sectionGroup >

 </configSections>

 <CUSTOMSECTION>
   <DEV configSource="DEV.config"/>
   <TEST configSource="TEST.config"/>
   <PROD configSource="PROD.config"/>

 </CUSTOMSECTION>

 <appSettings>
   <add key ="Environment" value="DEV"/>
 </appSettings >
</configuration>

===================================================

here is the DEV.config
===================================================
<DEV>
 <add key="SQl_ConString" value="ConnectionString for SQL"/>
 <add key="OLEDB_ConString" value="ConnectionString for OLEDB"/>
</DEV>
===================================================

here is the TEST.config
===================================================
<TEST>
 <add key="SQl_ConString" value="ConnectionString for SQL"/>
 <add key="OLEDB_ConString" value="ConnectionString for OLEDB"/>
</TEST>
===================================================

here is the PROD.config
===================================================
<PROD>
 <add key="SQl_ConString" value="ConnectionString for SQL"/>
 <add key="OLEDB_ConString" value="ConnectionString for OLEDB"/>
</PROD>
===================================================