On Windows, I got "Unable to delete directory". What's wrong?

On Windows, I got "Unable to delete directory". What's wrong?

For instance, clean could fail if you already have opened a command line with target as the current dir. Windows locks some ressources and you need to close the handles on these ressources. To skip these errors, you could call clean with the command line parameter -Dmaven.clean.failOnError=false. For more information, refer to Ignoring Errors page.

Sysinternals produced a number of utilities, like Process Explorer or Handle that help you to deal with Windows handles.