Workspace unavailable error in Eclipse

Problem

You open Eclipse or NSight and it greets you with this error:

Workspace unavailable
Workspace at in use or cannot be created, choose a different one

Solution

Eclipse creates a .metadata/.lock file in your workspace directory when it is open. If this file was not deleted when you closed Eclipse, you can get this error. Delete that file and you should be able to open Eclipse without any error.

Tried with: NSight 5.5.0 and Ubuntu 12.04 LTS