using Windows 8.1 with ZoneAlarm Extreme Security 12.0.104.000.
The symptoms are as follows: Windows explorer can see the list of network shares from, in my case, a mix of NAS shares and a couple of other Windows machines. Opening a share would usually enumerate the root directory of the share successfully but attempting to enumerate the files in any of the folders would cause the explorer progress bar to tick along for ages until finally I presume it timed out and windows would issue various, and inaccurate, messages such as "The network path was not found", "The specified network name is no longer available" or more frequently "You might not have permission to use this network resource. The specified network name is no longer available.".
Googling around to solve this always pointed the finger at the NAS drive usually as that's different to most normal set ups or suggesting that access rights weren't set correctly but this is not the case because my machine can't browse other Windows machines and not just the NAS and my Win7 and WinVista machines can access the NAS and each other just fine.
Uninstalling ZoneAlarm caused everything to work fine again so it's definitely ZA.