Cause its a used copy, Here's what i am missing: Coal, Water, invisible_bogey, redcorona, whitecorona, James' Driving Bogey, James Face Textures, James Cab, James's Leading Bogey, James's Whistle, The Tender loads okay
If you can't register because it's a used copy, your only option is to purchase an updated version of Trainz, register that (to your current account), and download the latest models from: http://si3d2009.jimdo.com/
No registered Trainz copy means no download, not that you could download content for TRS2006 anymore if you did register it.