Cant transport to molten core!

Anyone else having this problem? When I try to use the questgiver Lothlo Riftwalker (or whatever his name is) to transport to Molten core (yes ive done the attunment to the core quest) I keep getting a message that molten core cannot be entered on normal diffuculty. Ive tried reseting my difficulties, and reseting all instances but still no luck.

Ive also tried typing in the script to set dungeon diffuculty, no dice. Very frustrating. Can anyone help.