title: RollingFileAppender is not creating log file
body: <p>I have following <code>log4j.xml</code> file for my tomcat web application:</p>
  
  <pre><code>&lt;?xml version="1.0" encoding="UTF-8"?&gt;
  &lt;!DOCTYPE log4j:configuration PUBLIC "-//APACHE//DTD LOG4J 1.2//EN" "log4j.dtd"&gt;
  &lt;log4j:configuration xmlns:log4j="http://jakarta.apache.org/log4j/"&gt;
  &lt;!-- Appenders --&gt;
  &lt;appender name="console" class="org.apache.log4j.ConsoleAppender"&gt;
      &lt;param name="Target" value="System.out" /&gt;
      &lt;layout class="org.apache.log4j.PatternLayout"&gt;
          &lt;param name="ConversionPattern" 
                          value="%-5p: %d{ABSOLUTE} [%t] %c:%L - %m%n" /&gt;
      &lt;/layout&gt;
  &lt;/appender&gt;
  
  &lt;appender name="errorFileAppender" class="org.apache.log4j.RollingFileAppender"&gt;
      &lt;param name="threshold" value="error" /&gt;
      &lt;rollingPolicy class="org.apache.log4j.rolling.TimeBasedRollingPolicy"&gt;
          &lt;param name="FileNamePattern" 
                  value="${catalina.base}/logs/error.%d{yyyy-MM-dd_HH}.log"/&gt;
          &lt;param name="ActiveFileName" value="${catalina.base}/logs/error.log"/&gt;
      &lt;/rollingPolicy&gt;
      &lt;layout class="org.apache.log4j.PatternLayout"&gt;
          &lt;param name="ConversionPattern" 
                          value="%-5p: %d{ABSOLUTE} [%t] %c:%L - %m%n" /&gt;
      &lt;/layout&gt;
  &lt;/appender&gt;
  
  &lt;!-- Application Loggers --&gt;
  &lt;!-- some loggers --&gt;
  
  &lt;!-- Root Logger --&gt;
  &lt;root&gt;
      &lt;priority value="warn" /&gt;
      &lt;appender-ref ref="console" /&gt;
      &lt;appender-ref ref="errorFileAppender" /&gt;
  &lt;/root&gt;
  &lt;/log4j:configuration&gt;
  </code></pre>
  
  <p>With this configuration everything is logging to <code>catalina.out</code>.<br>
  But my purpose was also to log all errors to separate <code>error.log</code> which will be rolled hourly.<br>
  When I was using <code>FileAppender</code> <code>error.log</code> file is created and populated with errors logs. But when I switched to <code>RollingFileAppender</code> <code>error.log</code> file is not even created.</p>
  
  <p>Please help me with this configuration. I can not spot mistake here.</p>