just in case this helps. My problem was that the default settings for the boot disk were higher than my laptop (I know). I fixed the problem by changing the boot2docker-vm properties via the VirtualBox GUI. Soon, when I open the thr properties, I saw several warnings at the bottom of the dialog box, so I followed the prompt and resolved these warnings, saved the settings, and now I could launch the docker.
I changed the CPU from 4-> 1, memory from 2G to 1.5G and video memory up to 20M. Hope it helps.
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