servlet as error-page

I have tried to create a error-page servlet and I can't get it working properly.
This is my doGet() method:

public void doGet(HttpServletRequest request
                       ,HttpServletResponse response)
        throws ServletException, IOException {
 
        log("doGet invoked");
        PrintWriter pw = response.getWriter();
 
        String db = request.getParameter("db");
        if (db == null || db.equals("")) {
            db = "mysql";
        }
 
        Connection conn = null;
        try {
            Class.forName("com.mysql.jdbc.Driver").newInstance();
            conn = DriverManager.getConnection("jdbc:mysql:///" + db);
 
            pw.println("<html><head><title>Servlet output</title></head><body>");
 
            Statement stmt = conn.createStatement();
            ResultSet res = stmt.executeQuery("show databases");
            while (res.next()) {
                pw.println("<p><a href=\"SqlServlet?db=" + res.getString(1)
                         + "\">" + res.getString(1) + "</p>");;
            }
        } catch (SQLException ex) {
            throw new ServletException("Wrapped SQLException", ex);
        } catch (ClassNotFoundException ex) {
            log("ClassNotFoundException");
        } catch (InstantiationException ex) {
            log("InstantiationException");
        } catch (IllegalAccessException ex) {
            log("IllegalAccessException");
        }
        pw.println("</body></html>");
    }

And this is a part of my web.xml file:

When an SQL-error occurs, it seems like Tomcat can't find the servlet. The message in the log-file is:

When I remove the error-page tag then a standard error-page (including the nested SQLException) is shown.