I am about to sign off, I am sure you realise that our colleague RKinner, made noticeable progress with this, and I feel it best, as he stands above me in this area, to leave more until he returns
I was just checking with you a few things I had noticed, to try and help.
He will of course see what has been done, when he comes back.
The reason I asked about MSE and Avast is , as I am sure you know, two AV programs with real time protection, is not a good idea.
By a somewhat surprising coincidence I have been researching the use of UAC and have prepared a precis of the problems that may be encountered in turning it off - here are two excerpts from that
Certain applications, which make lots of system changes can fail to work once you turn on UAC after their installation and they will work if you install them with UAC turned on. The failures happen because, when UAC is turned off, the virtualization techniques used by UAC for all applications are inactive. This causes certain user settings and files to be installed to a different place and no longer work when UAC is turned back on. To avoid these problems, it is better to have UAC turned on at all times.
The biggest non-security problem comes about because many users disable UAC when they're setting up their machines, when installing their software, many older applications will happily write to Program Files as they're running with full rights to the machine, they'll store their data, and config files there, or in system locations in the registry.
This is a disaster waiting to happen, when UAC is re-enabled the applications will suddenly lose all of its config information and whatever else it has saved into Program Files as UAC redirects them to where they should be writing their data, in locations writable by standard users, such as ProgramData or AppData. Many applications will however happily recreate their information with the default settings. Some however will break horribly, I've run into situations where applications won't uninstall or install because its state has gotten so muddled due to the user disabling and enabling UAC over and over. They had to be manually removed from the system and then reinstalled.
I just begin to wonder if this may have caused some problems.
It appears the generally accepted answer, but NOT the real solution is, if it was off when certain applications were installed and those will not now work when it is ON, turn it off again, however it is as you will see a double edged sword.
In summary, as I said previously, I wish you the very best of luck with it, you deserve to have a solution for your dedication.
My colleague may have a view on this when he returns, but I am NOT saying it is the problem, only that it could well have a bearing on it.
Also post 103 reveals a stange behaviour does it not, it seems that one time something will work and then not, and then suddenly it works again. eg. Programs and Features.