Oops, thats what I get for running with scissors. 

Yes, the cert file is in pem format. Its the same file in use on my ldap server and all my servers and workstations that authenticate against it. I have an existing python 2.x script using the python-ldap(different from python3-ldap) module that uses this exact same file and works correctly. 

I've tested with the socket code above on python 2 and 3 and it works on my linux systems and on Windows XP. I only get this error on a Windows 7 system.