I'm submitting this as a To Do because I'm guessing this is an incomplete feature.
Windows 7 Ultimate, 64-bit, 32GB, 5960x, Nvidia Quadro FX 1800 (Primary) & GeForce 9800 GTX+ (Secondary)
Graphics Tablet: Wacom Bamboo Model: CTF-430 Driver Version 5.2.4-5
Ubuntu Linux (ubuntu-17.10-desktop-amd64) w/ Virtual Box Version 5.2.4 r119785 (Qt5.6.2))
Short description of error
Proxy render crash when building scene proxy.
Exact steps for others to reproduce the error
If you can't play the videos in your web browser, right-click the video --> copy link address (or equivalent) and play it in a media player like VLC.
blender-2.79.0 dbcc17 windows64
I managed to get the proxy rendered on my Lenovo T520 but my Lenovo X220 beeped when I started the proxy render:
The folder structure blender outputs is... well see for yourself (Main System)
This is the result after multiple failed attempts at building a proxy at different resolution percentages (with overwrite enabled)
As mentioned before I'm not too sure is this is a bug or an incomplete feature.