"Could not enter folder /media/sf_test": Trying to share folder between Kubuntu (guest) and Windows (host)

Question

I use VirtualBox 4.3.12 on Windows 7 SP1 x64 Ultimate, and have a VM running Kubuntu 14.10 Plasma 4.

I installed the Guest Additions, and added a shared folder:

After rebooting Kubuntu, I can see the shared folder in Dolphin, but can't access it:

Why?

Answer 1

It was a permission issue:

The solution is to add the current user to the vboxsf group:

sudo usermod -aG vboxsf $(whoami)