关于log4net自定义字段写入不进数据库的问题

<configuration>
  <startup>
    <supportedRuntime version="v4.0" sku=".NETFramework,Version=v4.0"/>
  </startup>
  <configSections>
    <section name="log4net" type="log4net.Config.Log4NetConfigurationSectionHandler,log4net"/>
  </configSections>
  <log4net>
    <logger name="Logger">
      <level value="All"/>
      <appender-ref ref="ADONetAppender"/>
    </logger>
    <!--<root>
            <level value="All" />
      <appender-ref ref="ADONetAppender" /> 
        </root>-->
    <appender name="ADONetAppender" type="log4net.Appender.ADONetAppender">
      <!--BufferSize为缓冲区大小-->
      <param name="BufferSize" value="1"/>
      <connectionType value="System.Data.SqlClient.SqlConnection, System.Data, Version=1.0.3300.0, Culture=neutral, PublicKeyToken=b77a5c561934e089"/>
      <connectionString value="database=***;server=.;User ID=sa;Password=***;"/>
      <commandText value="INSERT INTO SYS_Log ([LogTime],[Thread],[Level],[Logger],[Message],[UserID],[OperationID]) VALUES (@log_date, @thread, @log_level, @logger, @message,@UserID,@OperationID)"/>
      <parameter>
        <parameterName value="@log_date"/>
        <dbType value="DateTime"/>
        <layout type="log4net.Layout.RawTimeStampLayout"/>
      </parameter>
      <parameter>
        <parameterName value="@thread"/>
        <dbType value="String"/>
        <size value="255"/>
        <layout type="log4net.Layout.PatternLayout">
          <conversionPattern value="%thread"/>
        </layout>
      </parameter>
      <parameter>
        <parameterName value="@log_level"/>
        <dbType value="String"/>
        <size value="50"/>
        <layout type="log4net.Layout.PatternLayout">
          <conversionPattern value="%level"/>
        </layout>
      </parameter>
      <parameter>
        <parameterName value="@logger"/>
        <dbType value="String"/>
        <size value="255"/>
        <layout type="log4net.Layout.PatternLayout">
          <conversionPattern value="%logger"/>
        </layout>
      </parameter>
      <parameter>
        <parameterName value="@message"/>
        <dbType value="String"/>
        <size value="4000"/>
        <layout type="log4net.Layout.PatternLayout">
          <conversionPattern value="%message"/>
        </layout>
      </parameter>
      <parameter>
        <parameterName value="@UserID" />
        <dbType value="string" />
        <size value="255" />
        <layout type="Common.Logger.CustomLayout">
          <conversionPattern value="%UserID" />
        </layout>
      </parameter>
      <parameter>
        <parameterName value="@OperationID"/>
        <dbType value="string" />
        <size value="20" />
        <layout type="Common.Logger.CustomLayout">
          <conversionPattern value="%OperationID"/>
        </layout>
      </parameter>
    </appender>
  </log4net>
</configuration>

 <parameter>
        <parameterName value="@OperationID"/>
        <dbType value="Int" />
        <layout type="Common.Logger.CustomLayout">
          <conversionPattern value="%OperationID"/>
        </layout>
</parameter>