Windows error 5: Access is denied

[boh_1]

I'm having very similar issues but on Calibre startup on Windows 10. it used to work just fine and now it will not start without a Python error unless I "Run as Administrator" which has other restrictions. This is regardless of whether or not I turn off my A/V or set the environment variable above. here's the error dumpy:

calibre 3.12 [64bit]  embedded-python: True is64bit: True
Windows-10-10.0.15063-SP0 Windows ('64bit', 'WindowsPE')
('Windows', '10', '10.0.15063')
Python 2.7.12+
Windows: ('10', '10.0.15063', 'SP0', u'Multiprocessor Free')
Interface language: None
Successfully initialized third party plugins: X-Ray Creator (3, 1, 2) && Quality Check (1, 9, 11) && Kindle Collections (1, 7, 17)
Turning on automatic hidpi scaling
devicePixelRatio: 2.0
logicalDpi: 84.0 x 84.0
physicalDpi: 92.5388994307 x 92.6756756757
Using calibre Qt style: True
Python function terminated unexpectedly
  [Error 5] Access is denied (Error Code: 1)
Traceback (most recent call last):
  File "site.py", line 101, in main
  File "site.py", line 78, in run_entry_point
  File "site-packages\calibre\debug.py", line 260, in main
  File "site-packages\calibre\gui_launch.py", line 74, in calibre
  File "site-packages\calibre\gui2\main.py", line 542, in main
  File "site-packages\calibre\gui2\main.py", line 507, in create_listener
  File "multiprocessing\connection.py", line 130, in __init__
  File "multiprocessing\connection.py", line 342, in __init__
WindowsError: [Error 5] Access is denied

A long time ago and on an earlier version I had a similar issue which I fixed, alas I can't recall how. Is there any possibility that having other versions of Python run-times on my system (used by other programs) is causing some issue?

[DoctorOhh]

Moderator Notice
Moved to own thread, previous thread error was only on adding books. If I understand correctly this issue is on startup.

[kovidgoyal]

NO calibre uses its own private python. And that error literally means that something on your computer is blocking calibre from opening a socket to communicate with its worker process. The only known cause of that is security/antivirus/firewall programs.

[boh_1]

Okay, even all A/V completely disabled, I still see the same error. I will hack away at this and report any updates / fixes to this thread.