The Article is Currently Being Edited by Another Editor

If you have more than one editor at your Joomla site, you need to keep in mind that only one editor can edit an article at a time. So, once an editor has gone inside an article to make edits, the other editors will not be able to go in that article until the first editor has finished his or her editing.

But what might happen at times is that the editor who went in the article could end up not making any changes and rather than closing the article with the cancel button, he or she might just close the browser or browse away from the backend. This will result in the article being locked.

If this is the case, you simply need to go to Tools > Global Checkin. This will get rid of the locked status of any article which might have ended up staying as locked.