Are you using Mapster by any chance ?
If so, add the following to your InstanceMaps.lua file...
["Molten Front"] = 795,
["Firelands"] = 800,
The Firelands one must be in the Raids section under Cataclysm. Molten Front can be anywhere.
You can also update LibMapData from
Curse. Addon was last updated three weeks ago.