loadConfiguration() is called twice by tomcat -> exception

Hi,
During startup tomcat 3.2.4 (velocity 1.2 )  the Method 
loadConfiguration()  is called once.
All stuff  initialized very well.

Wenn i try to call the servlet with

http://localhost:8080/zerf

the loadConfiguration() is called a second time, with a Nullpointer-Exc 
in Line

String propsFile =  config.getInitParameter(INIT_PROPS_KEY); 

(The whole code-sniplet is at the bottom of this Mail)

Whats going wrong????

My Module is located in: tomcat_home/webapps/zerf/...
The class is located in:  
tomcat_home/webapps/zerf/WEB-INF/classes/zerf/znSignController.class

My web.xml:

<web-app>
   <servlet>
       <servlet-name>zerf</servlet-name>
       <servlet-class>zerf.ZnSignController</servlet-class>
     <init-param>
       <param-name>properties</param-name>
       <param-value>conf\zerf_config.properties</param-value>
     </init-param>
     <load-on-startup>1</load-on-startup>
   </servlet>
   <session-config>
       <session-timeout>
           30
       </session-timeout>
   </session-config>
   <welcome-file-list>
   <welcome-file>
           index.jsp
       </welcome-file>
   <welcome-file>
           index.html
       </welcome-file>
   <welcome-file>
           index.htm
       </welcome-file>
   </welcome-file-list>
</web-app>   

The loadConfiguaration Method:

   protected Properties loadConfiguration(ServletConfig config)
   throws IOException, FileNotFoundException {
      
       System.out.println("---------- Load ZERF Konfiguration: ");
      
       // web.xml auslesen:
       String propsFile =  config.getInitParameter(INIT_PROPS_KEY);
       System.out.println("Reading Path from Propertie-File from 
web.xml: " + propsFile);
     
       /* now convert to an absolute path relative to the webapp root
        * This will work in a decently implemented servlet 2.2
        * container like Tomcat.
        */
       if (propsFile != null){
           String realPath = getServletContext().getRealPath(propsFile);
           if (realPath != null) propsFile = realPath;
       }
      
       Properties p = new Properties();

       try{
           System.out.println("Load Properties from: " + propsFile);
           p.load(new java.io.FileInputStream(propsFile));
       }catch (Exception e){
           handleException(e, "Error while loading Properties");
       }

      /* now, lets get the two elements we care about, the
       * template path and the log, and fix those from relative
       * to the webapp root, to absolute on the filesystem, which is
       * what velocity needs
       */
      String path = p.getProperty(Velocity.FILE_RESOURCE_LOADER_PATH);

      if (path!=null){
          path = getServletContext().getRealPath(path);
          p.setProperty(Velocity.FILE_RESOURCE_LOADER_PATH, path);
      }

      path = p.getProperty("runtime.log");

      if (path != null){
          path = getServletContext().getRealPath(path);
          p.setProperty("runtime.log", path);
      }
      
      System.out.println("Path to Templates: " + 
p.getProperty(Velocity.FILE_RESOURCE_LOADER_PATH));
      System.out.println("Path to Log-File: " + 
p.getProperty("runtime.log"));
      System.out.println("-----------------------------------");
      return p;
      
   }