Foros del Web - Variable global para todas las páginas en ASP.NET

Exactamente donde puedo poner ese código, porque donde quiera que lo coloco me da error.

Este es mi Web.Config:
Código:
<?xml version="1.0" encoding="utf-8"?>

<configuration>

    

  <system.web>
 

    <!--  DYNAMIC DEBUG COMPILATION

          Set compilation debug="true" to insert debugging symbols (.pdb information)

          into the compiled page. Because this creates a larger file that executes

          more slowly, you should set this value to true only when debugging and to

          false at all other times. For more information, refer to the documentation about

          debugging ASP.NET files.

    -->

    <compilation defaultLanguage="vb" debug="true"><assemblies><add assembly="CrystalDecisions.CrystalReports.Engine, Version=9.1.3300.0, Culture=neutral, PublicKeyToken=692fbea5521e1304"/><add assembly="CrystalDecisions.ReportSource, Version=9.1.3300.0, Culture=neutral, PublicKeyToken=692fbea5521e1304"/><add assembly="CrystalDecisions.Shared, Version=9.1.3300.0, Culture=neutral, PublicKeyToken=692fbea5521e1304"/><add assembly="CrystalDecisions.Web, Version=9.1.3300.0, Culture=neutral, PublicKeyToken=692fbea5521e1304"/></assemblies></compilation>
 

    <!--  CUSTOM ERROR MESSAGES

          Set customErrors mode="On" or "RemoteOnly" to enable custom error messages, "Off" to disable. 

          Add <error> tags for each of the errors you want to handle.

    -->

    <customErrors mode="Off"/>
 

    <!--  AUTHENTICATION 

          This section sets the authentication policies of the application. Possible modes are "Windows", 

          "Forms", "Passport" and "None"

    -->

    <authentication mode="Windows"/> 
 
 

    <!--  AUTHORIZATION 

          This section sets the authorization policies of the application. You can allow or deny access

          to application resources by user or role. Wildcards: "*" mean everyone, "?" means anonymous 

          (unauthenticated) users.

    -->

    <authorization>

        <allow users="*"/> <!-- Allow all users -->
 

            <!--  <allow     users="[comma separated list of users]"

                             roles="[comma separated list of roles]"/>

                  <deny      users="[comma separated list of users]"

                             roles="[comma separated list of roles]"/>

            -->

    </authorization>
 

    <!--  APPLICATION-LEVEL TRACE LOGGING

          Application-level tracing enables trace log output for every page within an application. 

          Set trace enabled="true" to enable application trace logging.  If pageOutput="true", the

          trace information will be displayed at the bottom of each page.  Otherwise, you can view the 

          application trace log by browsing the "trace.axd" page from your web application

          root. 

    -->

    <trace enabled="false" requestLimit="10" pageOutput="false" traceMode="SortByTime" localOnly="true"/>
 
 

    <!--  SESSION STATE SETTINGS

          By default ASP.NET uses cookies to identify which requests belong to a particular session. 

          If cookies are not available, a session can be tracked by adding a session identifier to the URL. 

          To disable cookies, set sessionState cookieless="true".

    -->

    <sessionState mode="InProc" stateConnectionString="tcpip=127.0.0.1:42424" sqlConnectionString="data source=127.0.0.1;user id=sa;password=" cookieless="false" timeout="20"/>
 

    <!--  GLOBALIZATION

          This section sets the globalization settings of the application. 

    -->

    <globalization requestEncoding="utf-8" responseEncoding="utf-8"/>

  </system.web>

</configuration>