I'm sorry to hear that you are having problems with JuiceboxBuilder-Pro.
Hopefully my notes below will help.

First of all, it might help to know exactly how the error message is triggered.
Does the error message occur as soon as you click the 'New Gallery' button or is there a set of steps that seems to cause the problem (and if so, what are they)?

If the error message occurs when you try to add many images to JuiceboxBuilder-Pro at once, then Adobe AIR (the platform on which JuiceboxBuilder-Pro runs) may not be able to allocate enough memory for the task at hand. Even if your computer has plenty of free RAM, Adobe AIR applications are limited to around 1GB of memory allocation. The workaround is to add your images in smaller batches.

If this is not the case, then try uninstalling and then reinstalling JuiceboxBuilder-Pro to see if this helps.
Please follow the procedure below.

(1) Uninstall JuiceboxBuilder-Pro.
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 (if they exist) from your hard drive:
Mac:
/Applications/JuiceboxBuilder-Pro.app/
/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) Reinstall JuiceboxBuilder-Pro following the instructions here.

(I realise that you are using a Windows PC 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 try uninstalling and reinstalling Adobe AIR itself, too.
You can download the latest version (v30.0) from here.

Also, it might help to check the Windows Event Viewer.
There should be an entry in the 'Windows Logs -> System' section corresponding to the crash. (The easiest way to find the relevant entry is to take a note of the time of the crash and look for entries around that time in the log.)
If you highlight the relevant entry, then the details displayed in the 'General' and 'Details' tabs should help to pinpoint the exact cause of the problem.
If you post these details in this forum thread, I might be able to help further.

However, hopefully a complete uninstall and reinstall of JuiceboxBiilder-Pro will solve your problem.

Tried adding the images in smaller batches and it worked!