If you get following message in your Joomla! administration: Item is currently being edited by another user (or similar with the same meaning), then it seems, like the item (article, item of other extension - e.g. image, category, file, ...) is edited by other user or user who have edited this item, didn't save it or close it properly. It can happen, then when you leave your work while editing an item, then next time such is blocked.
If you have rights to do:
  • you can click on lock icon next to item in item's list to unlock it or
  • go to: Site - Maintenance - Global Check-in. Select item and click on Check-in button to unlock it.