I use Virtualbox 4.3.20 with Ubuntu 14.01 image. Host OS is Windows 8.1. Bidirectional drag'n drop used to work before but now it won't after upgrading to these versions from previous versions. What can I do to resolve the problem?
"Drag and Drop" was introduced with the guest additions in Virtual Box 5.0. with some limitations:
At the moment drag and drop is implemented for Windows- and X-Windows-based systems, both, on host and guest side. As X-Windows sports different drag and drop protocols only the most used one, XDND, is supported for now.VirtualBox Manual
In addition to that only drag & drop of simple text, or files and directories of the file manager not running with administrative permissions is supported.
Preliminary experimental versions of Virtual Box "Drag'N'Drop" to a Linux guest only were introduced in version 4.2 .
According to the Release notes: https://www.virtualbox.org/wiki/Changelog-4.2
"Added experimental support for Drag'n'drop from the host to Linux guests. Support for more guests and for guest-to-host is planned."
I did not see any newer release notes indicating that status had changed.
So, Drag 'n' Drop will only work 1 way. Try enabling only "host to guest". Also, because of this reason it may be more efficient to just use a shared folder and move files back and forth that way.