Error: Failed to create the VirtualBox COM object

[bruce.desertrat]

For one user of a Mac (10.9.2) trying to start Virtualbox results in the following error:

Failed to create the VirtualBox COM object.
Callee RC: NS_BASE_STREAM_WOULD_BLOCK

It works for other users on the Mac.

I have:

uninstalled VirtualBox with the script provided
Re-installed virtualbox
deleted the users org.virtualbox.app.VirtualBox.plist and VirtualVBoxVM.plist files
deleted the users org.virtualbox.app.VirtualBox.savedState and VirtualBoxVM.savedState files

And I still get the issue. It runs just fine for me. VirtualBox Manager doesn't start with the above error for her.

all involved users are administrators.