The NWeekdayOfMonth() function in the PEAR Date::Calc class calls 2 other Date::Calc functions using incorrect parameters.  This produces results that are almost always invalid.

Line 1246 of Date/Calc.php is:
  $DOW1 = Date_Calc::dayOfWeek($month,$year,$DOW1day);
when it should be:
  $DOW1 = Date_Calc::dayOfWeek($DOW1day,$month,$year);

Line 1254 of Date/Calc.php is:
  return(Date_Calc::dateFormat($month,$year,$wdate,$format));
when it should be:
  return(Date_Calc::dateFormat($wdate,$month,$year,$format));

Here is the patch:
-------------------------------------

--- Calc.php.orig       Tue Sep 10 09:51:08 2002
+++ Calc.php    Tue Sep 10 09:51:09 2002
@@ -1243,7 +1243,7 @@
         $month = sprintf("%02d",$month);
 
         $DOW1day = sprintf("%02d",(($occurance - 1) * 7 + 1));
-        $DOW1 = Date_Calc::dayOfWeek($month,$year,$DOW1day);
+        $DOW1 = Date_Calc::dayOfWeek($DOW1day,$month,$year);
 
         $wdate = ($occurance - 1) * 7 + 1 +
                 (7 + $dayOfWeek - $DOW1) % 7;
@@ -1251,7 +1251,7 @@
         if( $wdate > Date_Calc::daysInMonth($month,$year))
                 return -1;
         else
-                return(Date_Calc::dateFormat($month,$year,$wdate,$format));
+                return(Date_Calc::dateFormat($wdate,$month,$year,$format));
 
     } // end func NWeekdayOfMonth