Errors when updating Blend4Web version

Two computers I use at work need to be updated to Blend4Web 16.1. They currently are running 15.11 on OS X 10.10.4.

At first I tried to move out the old SDK folder, put the new one in its place, and start Blender. This resulted in a warning that the scripts path is deprecated. "No problem", I thought. I have fixed this on other machines I updated to 16.1 by shortening the file path to the SDK's root folder. But this time when I tried to save the settings I got an error:

Cannot change old file (file saved with @)

Update: I have since discovered that this occurs when attempting to save any kind of Blender settings, not only Blend4Web settings.

I thought maybe I need to change permissions somewhere, so I gave Read & Write permissions to the SDK folder, ~/Library/Application Support/Blender/2.76, and Blender.app. This didn't make any difference though.

I also tried removing the Blend4Web add-on so I could reinstall it, but when I tried to remove it I got this other error:

Traceback (most recent call last):
  File "/Applications/Blender 2.76b/Blender 2.76b.app/Contents/Resources/2.76/scripts/startup/bl_operators/wm.py", line 2090, in execute
    shutil.rmtree(path)
  File "/Applications/Blender 2.76b/Blender 2.76b.app/Contents/Resources/2.76/python/lib/python3.4/shutil.py", line 477, in rmtree
    return _rmtree_unsafe(path, onerror)
  File "/Applications/Blender 2.76b/Blender 2.76b.app/Contents/Resources/2.76/python/lib/python3.4/shutil.py", line 372, in _rmtree_unsafe
    onerror(os.unlink, fullname, sys.exc_info())
  File "/Applications/Blender 2.76b/Blender 2.76b.app/Contents/Resources/2.76/python/lib/python3.4/shutil.py", line 370, in _rmtree_unsafe
    os.unlink(fullname)
PermissionError: [Errno 13] Permission denied: '/Users/user/Documents/blend4web_sdk_free/blender_scripts/addons/blend4web/__init__.py'

location: <unknown location>:-1

What do I need to do to resolve this and update successfully?
Thanks in advance for any help.

Hi,

Update: I have since discovered that this occurs when attempting to save any kind of Blender settings, not only Blend4Web settings.

You may want to re-install Blender on that computer.

I also tried removing the Blend4Web add-on so I could reinstall it, but when I tried to remove it I got this other error:

This command only valid for removing the standalone add-on, not the SDK. Try to fresh-install the SDK.

Thank you for the advice.

I have a few ideas about what may have caused the problem.

1) The accounts with the problem have OS X's Parental Controls enabled, to prevent students from changing system settings. Parental Controls may have restricted the capabilities in some way, although when I originally installed B4W it was not a problem.

2) Maybe some contents of the SDK were corrupted or permissions changed during the process of being copied. I unzipped the folder and then sent it over Air Drop, but maybe I should have sent it while still zipped as a single file.
There is a unique copy of the SDK for each user, so it's possible that the some users have working SDKs and some don't.

3) Maybe I messed it up by updating Blend4Web incorrectly.

The problem seems to be centered around not having write permissions to some folder(s), either within the SDK or within Blender. Another symptom is that Fast Preview can't be launched because the necessary temp files can't be written.

I should mention that users with admin privileges are not experiencing any problems.
One thing I still want to try is making the problem users admins, rebooting, then updating.

It will be a few days before I can continue troubleshooting it. For now, my personal installations of B4W are working fine.
Thanks!

Status update:

I changed the users into admins, rebooted, uninstalled B4W, restarted Blender, reinstalled B4W starting from a freshly downloaded .zip of the SDK (first specifying the add-on path, then relaunching Blender and enabling the add-on, as described in B4W documentation), and then it was fixed.

Even after changing the users from admin back to normal everything appears to be working fine.