The latest build of NSolV8 as of 15 Dec 2022 is V8.1.11
NSolVx is no longer being sold, but a download link is provided for registered users.

This appears to be related to the increasingly strict ways that Windows Defender and other anti-virus programs manage program access, especially for specialized programs such as NSolV8.
One user sent in the following instructions to manage via Windows:
Select Start > Settings > Update & Security > Windows Security > Virus & threat protection. Under Virus & threat protection settings, select Manage settings. Under Controlled folder access, select Manage Controlled folder access. From there I selected Allow An App Through Controlled Folder Access then Add An Allowed App and browsed for the NSOL8.exe.
There are similar procedures for other anti-virus programs.

The databases are found in c:\nsolvx\db folder. The easiest way to back this up is to compress the entire c:\nsolvx folder into a single file, add a date to it and then move the compressed (zip) file to a place that you normally include in your backups.

Sort of.  In ALR calculations using PWM controllers, all amp-hour losses are lumped together under system losses.  5% is a typical coulombic loss for a battery, so the coulombic efficiency would be 95%.  Another 5% is to account for mismatch, soiling, etc. so the total losses are 10%.
In the MPPT model, the average charge voltage of the battery and the voltage drop between battery and array are also factored in. The charge controller efficiency is figured separately.

Yes. Clearness is the ratio between the global horizontal insolation (GHI – from the site tab) and the extra-terrestrial insolation (calculated). It is used in the correlation to split GHI into direct and diffuse irradiance in order to do the tilt calculations.

The calculations use a published correlation (ref Page – “Diffuse Fraction Correlations,” Solar Energy Vol 45, No. 1, pp. 1-7, 1990 ) to divide the GHI insolation into direct and diffuse components.  As the array is tilted up, the direct component is typically increased the closer the tilt is to aiming at the elevation of the sun.  Conversely, the tilted array “sees” less of the rest of the sky, so the diffuse component is typically reduced.  Reflection is a simple percentage of the direct.
The following link does a decent job explaining this in a simple manner.
https://www.folsomlabs.com/modeling/environment/irradiance_calculation
For more details, see something like
http://www.amazon.com/Solar-Engineering-Thermal-Processes-Duffie/dp/0470873663/ref=sr_1_1?s=books&ie=UTF8&qid=1462917171&sr=1-1
I own this book and have used it extensively, along with a number of old papers from Solar Energy Journal.