Logging in and out sometimes helps. You can try reinstalling the Dock. dde-dock I hope you took note of the Tip when installing will say Installing Deepin on a virtual machine will affect its performance.Though my dock in Vbox seems to function okay.
One thing I do on Virtual box is always Take a Snapshot of the system after first install.

Well, I didn't mention it was giving me repeated errors with "deepin system updates", so I tried running sudo apt-get install, then sudo apt-get upgrade. This upgraded a number of things, and the system said restart required, upon restarting it's back, I wouldn't be entirely surprised if it disappears again, but now I can get back to work in Deepin : ' )

Okay let us know how it goes. And for other members reading this post I uploaded a screen shot of the message you get when installing on a virtual machine.

Hmmm booted up and it was gone again, tried uninstalling reinstalling dock (dde-dock), logging out, log out went to a glitched black screen, had to force restart my virtual box. Upon restarting I get the same glitched screen. Booted into recovery mode, and tried a number of options, which each eventually froze. Looks like my virtual machine is shot, no harm done, only had a test dev environment set up in it. Any troubleshooting tips? I might just revisit it with a fresh install of a newer version later, I love the interface and specifically the dock/efficiency mode options.

Edited by dance707 at 2016-3-5 20:58

We do normally do not address installing Deepin in a Virtual Box. As it is not really recommend. I do not know if it is problem with your Host system or Virtual Box or with the install of Deepin 15.1 or your settings in the Virtual Box. My Deepin install in a Virual Box seems to be okay but I not really use it.
From my experience with Virtual Box with any Distro. I always take a snapshot after first install of and additional snapshot after any major upgrades. That way you can easily restore to a previous point and not have to reinstall again. That is one of the better features in Virtual Box.

Also if you have not read in forum, next week we should have a new  ISO for Deepin 15.1.1 that will contain the latest updates and hopefully additional patches.