Well, the Deck Garage is another one of those concepts we had going that fizzled right around the same time as the original TCotD. The area was for Deck Mechanics to tune-up people's decks who submitted them to the moderator of that area. The reason you can't post there is because only Deck Mechanics have permission to start threads there.
If you want help from the general membership with your deck, you'd need to post it in either the Advanced Format or Traditional Format sections, whichever is appropriate.