Lockbox Contained No Loot Or Was Unable To Be Opened

Lockboxes received from in-game content as a random drop must be unlocked before using. Rogues have a "Pick Lock" spell that works for these: depending on the WOW variant, the skill must be leveled up or is automatically set depending on character level. Locks can be picked by rogues for other characters through the in-game trade feature in the "will not trade" slot. There are also various in-game items from professions and other sources that other classes can use to open lockboxes without assistance.

If you are unable to open a lockbox, make sure it doesn't have the word Locked in the tooltip when you mouseover the item. 

If you have an unlocked box that you can't open, it may be due to issues with your User Interface, including your AddOns. Try updating your AddOns. If that doesn't fix the issue, disable all AddOns. Finally, you may need to reset your UI altogether to resolve the issue.

If you have reset your user interface and are still unable to open your box, please report the issue as a bug.