Python ldap3 LDAPSocketOpenError无法发送消息，套接字未打开

我在Python中编码，ldap3试图在CentOS上的OpenLDAP中创建用户。我的本地开发机器运行的是Windows 8 64位。以下是我的代码。Python ldap3 LDAPSocketOpenError无法发送消息，套接字未打开

from ldap3 import Server, Connection, ALL 

# define the server 
s = Server('ldap://ldap.abcd.com:389', get_info=ALL) 

# define the connection 
c = Connection(s, user='cn=Manager,dc=mydomain,dc=com', password='Super1') 

# perform the Add operation 
c.add('uid=user3,ou=People,dc=abcd,dc=com',['person','organizationalPerson','inetOrgPerson', 'posixGroup', 'top','shadowAccount'], {'givenName': 'user3firstname','sn': 'user3lastname', 'uidNumber' : 520,'gidNumber' : 521,'uid': 'user3','cn': 'user3user3lastname'}) 

# close the connection 
c.unbind()

服务器和连接类正常工作。我猜是因为如果我只运行那2条语句，它并没有在下面产生一个错误。

LDAPSocketOpenError at /adminservice/users/ 
unable to send message, socket is not open 
Request Method: GET 
Request URL: http://127.0.0.1:8000/adminservice/users/ 
Django Version: 1.8.4 
Exception Type: LDAPSocketOpenError 
Exception Value:  
unable to send message, socket is not open 
Exception Location: C:\Python35\lib\site-packages\ldap3\strategy\base.py in send, line 299 
Python Executable: C:\Python35\python.exe 
Python Version: 3.5.1 
Python Path:  
['D:\\sourcecode\\idp', 
'D:\\sourcecode\\utils-drf-public-api', 
'C:\\Python26', 
'C:\\Python35\\python35.zip', 
'C:\\Python35\\DLLs', 
'C:\\Python35\\lib', 
'C:\\Python35', 
'C:\\Python35\\lib\\site-packages'] 
Server time: Fri, 13 May 2016 17:02:08 +0700