sslerror: (8, 'EOF occurred in violation of protocol')

[Robert]

I'm using the https-protocol. On my systems and network everything works ok.
But on some connections from some other users' computers/network I get this
error (Python 2.3.5 on Windows):

Traceback (most recent call last):
  File "<interactive input>", line 1, in ?
  File "ClientCookie\_urllib2_support.pyo", line 524, in open
  File "ClientCookie\_urllib2_support.pyo", line 424, in http_response
  File "ClientCookie\_urllib2_support.pyo", line 541, in error
  File "urllib2.pyo", line 306, in _call_chain
  File "ClientCookie\_urllib2_support.pyo", line 185, in http_error_302
  File "ClientCookie\_urllib2_support.pyo", line 518, in open
  File "urllib2.pyo", line 326, in open
  File "urllib2.pyo", line 306, in _call_chain
  File "ClientCookie\_urllib2_support.pyo", line 759, in https_open
  File "ClientCookie\_urllib2_support.pyo", line 608, in do_open
  File "httplib.pyo", line 712, in endheaders
  File "httplib.pyo", line 597, in _send_output
  File "httplib.pyo", line 564, in send
  File "httplib.pyo", line 985, in connect
  File "socket.pyo", line 73, in ssl
sslerror: (8, 'EOF occurred in violation of protocol')


The target-server is always the same and ok. but different
client-OS(Windows)/proxies/firewalls/routers are in use.
What is the nature of this error? How is it possible that an EOF in
ssl-connections (during connect?) occures?
What can be done to handle/circumvent that problem?

Robert