Some of the eclipse editor's messages are very annoying and difficult to understand.
One such message is: eclipse workspace in use or cannot be created. And it offer no solution to this problem. I have to manually solve this. I got this problem when my network drive was unaccessible.
Go to C:\eclipse\configuration\.settings\org.eclipse.ui.ide.prefs.
Open this file in text editor and check the RECENT_WORKSPACES directive. Delete the overlapping directive and your problem may be solved.
If not then delete all value part. Here you will see \n as workspace separator.
Above problem- 'Workspace in use', may also come, if your workspace in on network and are not connected.
You can also check the Task Manager in Window operating system. If eclipse.exe is already running then may get the same error.