Everytime we try to activate the Inferno mode… the Twilight mode gets started.
Its impossible to get the Achievements for completing the dungeons on Inferno mode this way..
or collecting stuff for transmogs etc…
I thought you can collect transmog from inferno heroics by swapping twilight heroic dungeon currency at vendor.
As for achievements it might be, that you and 4 other people need to have a lvl 85 characters to queue there.