This is an issue with OSX, not LOTRO. It is Apple's Gatekeeper generating a bogus error message. It is an Apple Bug!
Originally Posted by ReakCyberJ
It should be giving you the option to approve the use of the downloaded application, but it is not doing that.
You need to disable Gatekeeper in "System Preferences/Security & Privacy/General"; Click the lock to authenticate, then click "Anywhere."
Bill Magill - Mac Player - Old Timers Guild- Gladden:
Valamar: Dwarf Hunter - Level 100
Valdicta: Dwarf Rune-keeper - Level 100
Valanne: Beorning - Level 80