[AvatarOfLight]

Oh well, all I can do is recap.
This problem has been around for a while and afaik it's always a typo.
Either something simple is going wrong or there's nothing I can do to help.

Obviously, make sure your game is fully patched.
I assume you're playing HOTU.
The console is case sensitive so don't forget proper capitalization.

You go to the console.

You enter "DebugMode 1" command

You move your cursor some place in front of your character to someplace an item can be safely spawned.

You enter "dm_spawnitem x2_it_cmat_adam" command

Pick up the item from the ground where your cursor is.

If this doens't work, try some other console commands to see where the problem lies.
Is it correct you want a "bar of adamantine"? I saw no reference to a chunk, could be me.