It seems that maybe a corrupt settings/snapshots file is preventing Mosaico from working correctly. Please try to do the following in order to have a fresh install of Mosaico:

1. Close Mosaico
2. Delete these files if they exist:
— C:\Users\Public\AppData\Local\mosaico\license.dat
— C:\Users\USERNAME\AppData\Local\mosaico\SoulidStudio\Mosaico\license.dat
3. Delete C:\Users\USERNAME\AppData\Local\mosaico\SoulidStudio\Mosaico\ (this will wipe your settings, so feel free to make a backup first)
4. Uninstall any previous version of Mosaico
5. Delete any key in the registry containing “Mosaico” (do this at your own risk, though)
6. Reboot your PC (or virtual machine)
7. Download and install the latest version available at http://www.soulidstudio.com

I hope this proves helpful.