log4j: log4j:ERROR Attempted to append to closed appender named [stdout]

What is meant by "Attempted to append to closed appender " ?

The following is a small part of my log4j.xml file

<appender name="stdout" class="org.apache.log4j.ConsoleAppender">
    <param name="Threshold" value="TRACE" />
    <param name="Target" value="System.out" />
    <layout class="org.apache.log4j.PatternLayout">
        <param name="ConversionPattern" value="%d %-5p: %m%n" />
    </layout>
</appender>

<logger name="java.sql" additivity="false">
    <level value="trace" />
    <appender-ref ref="stdout" />
</logger>

I am trying to print some sql queries out , but I am getting the above error . Am I missing something ?