The error message you are getting from Adobe AIR (Error# 5100) is a generic 'install failed' message which, unfortunately, does help to pinpoint the exact problem.
However, I hope that my notes below will help.

First of all, I would encourage you to use the latest version of Juicebox-Pro (v1.5.1) as many bugs have been fixed since v1.5.0. Please see the Version History for details.
Full instructions for downloading the latest version can be found on the Upgrading Juicebox support page.

If you have been able to successfully extract the 'juicebox_pro_1.5.1.zip' file without any errors, then it is unlikely that there is a problem with the 'JuiceboxBuilder-Pro.air' installation file.
However, if you would like to make sure that your 'JuiceboxBuilder-Pro.air' file is OK, then it should have the following properties:
Filename: JuiceboxBuilder-Pro.air
File Size: 1,387,727 bytes
MD5: 8a4b4ed6a07a16c0c057b35470f2e968
SHA1: f0ce907b4deb82155e0894f14cd23e848d020c9c

You can check the MD5 and SHA1 hashes of files with a free program such as HashCalc: http://www.slavasoft.com/hashcalc/

If your own 'JuiceboxBuilder-Pro.air' file does not have the properties above, then please try re-downloading the Juicebox-Pro v1.5.1 zip file.

As long as your 'JuiceboxBuilder-Pro.air' file is OK, I would recommend that you try uninstalling and reinstalling both Adobe AIR and JuiceboxBuilder-Pro to see if a fresh installation helps.

Please try the following:

(1) Uninstall JuiceboxBuilder-Pro (if you can).
Mac: Delete the 'JuiceboxBuilder-Pro' file from the Applications folder and empty your Trash.
Windows: Use the uninstaller in the 'Control Panel -> Programs -> Uninstall a program...' list.

(2) After uninstalling JuiceboxBuilder-Pro, please check that there are no files are left behind (even from a failed installation) by manually deleting the following folders from your hard drive:
Mac:
/Users/Username/Library/Application Support/Adobe/AIR/ELS/JuiceboxBuilder-Pro
/Users/Username/Library/Preferences/JuiceboxBuilder-Pro
Windows:
C:\Program Files (x86)\JuiceboxBuilder-Pro
C:\Users\Username\AppData\Roaming\Adobe\AIR\ELS\JuiceboxBuilder-Pro
C:\Users\Username\AppData\Roaming\JuiceboxBuilder-Pro
C:\Users\Username\Documents\JuiceboxBuilder-Pro
You may need to show hidden files to find some of the above locations in Windows File Explorer.

(3) Also, please follow the procedure above (Steps #1 - #2) for JuiceboxBuilder-Lite, too (if you have it installed).
JuiceboxBuilder-Lite and JuiceboxBuilder-Pro can both be installed and run side by side on the same computer but, being that you are experiencing problems, it might be wise to completely clear your system of all JuiceboxBuilder files before trying to reinstall JuiceboxBuilder-Pro.

(4) Uninstall Adobe AIR (again, via the control panel).

(5) Reinstall Adobe AIR (as an administrator).
You can download the current version of Adobe AIR from here.
When reinstalling Adobe AIR, instead of just double-clicking the 'AdobeAIRInstaller.exe' installation file, right-click the file and select 'Run as administrator'.

(6) Reinstall JuiceboxBuilder-Pro following the instructions here.

(I realise that you are using PCs but I've included notes for Mac above, too, in case any Mac users are experiencing similar issues and are reading this forum thread.)

Hopefully this will help.
If not, then here are a few more things to try that might help.

(1) Manually choose for the 'JuiceboxBuilder-Pro.air' file to be opened with the Adobe AIR Application Installer.
Right-click the 'JuiceboxBuilder-Pro.air' file and select 'Open with...'.
Now choose 'Adobe AIR Application Installer' if it is listed. If it is not listed, click 'More apps', scroll down to the bottom of the list, click 'Look for another app on this PC' and navigate to (and select) the 'C:\Program Files (x86)\Common Files\Adobe AIR\Versions\1.0\Adobe AIR Application Installer.exe' file.

(2) Try temporarily turning off any security software that you might have installed (or make an exception within the software for the 'JuiceboxBulder-Pro.air' file) in case this is somehow interfering with the JuiceboxBuilder-Pro installation process. (Another user who reported the Error# 5100 message found that the problem was caused by Bitdefender Total 2017.)

(3) Maybe the problem is somehow connected to UAC (User Account Control).
Try temporarily turning off UAC (set it to 'Never Notify') before attempting to install JuiceboxBuilder-Pro.
Instructions for changing the UAC setting can be found here.
If this allows you to install JuiceboxBuilder-Pro, then you can turn on UAC again afterwards.

(4) Try creating a new User Account (make sure it is an Administrator Account), log into this new account and try installing JuiceboxBuilder-Pro from there.

It is certainly strange that you have been unable to install JuiceboxBuilder-Pro on two different PCs.
I have never encountered the Error# 5100 message myself so it sounds like there may be something common to both your PCs which might be causing the problem (perhaps a similar security or anti-virus program).

I hope that the suggestions above help you to successfully install JuiceboxBuilder-Pro.
Please let me know how you get on and if you need any further assistance.

You're welcome!

Temporarily turning off Bitdefender whilst installing JuiceboxBuilder-Pro (or making an exception in Bitdefender for the 'JuiceboxBuilder-Pro.air' installation file) would be the first thing I'd try.
Hopefully this will resolve your problem and allow you to successfully install JuiceboxBuilder-Pro.

@kuwaha

Do you get exactly the same error message as the original poster ("Code: 5100") or a different error message?

If you have not already done so, please try following the procedure noted above (to uninstall both JuiceboxBuilder-Lite and JuiceboxBuilder-Pro and then manually delete all the folders I listed before before attempting to install JuiceboxBuilder-Pro v1.5.1).

Have you also tried the additional suggestions, such as creating a new administrative user account and trying to install and run JuiceboxBuilder-Pro v1.5.1 from there?

If you continue to experience difficulties, please let me know how far you get into the procedure and what error message (if any) you encounter along the way.
Also, please let me know what operating system you use.