Problem with threading: can't start new thread

[sufrank]

I am doing stress test with python using threading, I have encountered 
the can't start new thread problem when running the script.
The system is Linux, python version 2.4

Traceback (most recent call last):
  File "./imap_test.py", line 38, in ?
    current.start()
  File "/usr/lib/python2.4/threading.py", line 416, in start
    _start_new_thread(self.__bootstrap, ())
thread.error: can't start new thread


Part of my testing scripts(python) is as followed:

#!/usr/bin/python

import const;
import imap_pattern;

import os
import re
import time
import sys
from threading import Thread
import logging

Userno_Max = 1000
class client(Thread):
    def __init__ (self,ID,type,username):
        Thread.__init__(self)
        self.username = username
        self.type = type
        self.ID = ID
    def run(self):
        print self.ID
   
        myTest = imap_pattern.imap_pattern(self.ID)
        myTest.run_pattern(self.type,self.username)

if __name__ == '__main__':
  print time.ctime()
  Users = int(sys.argv[1])
  Period = float(sys.argv[2])

   
    id = 1
    for host in range(0,1000):
        username = "%s%d@%s" %(const.Username_Prefix, id % Userno_Max, 
const.Domain)
        current = client(id,1,username)
        current.start()
        id += 1