Stew2000,
I've had no problems uninstalling & re-installing 2004 & 2006.
The registration process has to be completed logically:-
1) on installation (or indeed re-installation) the install program will request you to enter the CD-Key (the long one).
This verifies that you have a valid product.
2) When you first register with Planet Auran, you need to enter this CD-Key so that your username is linked with this CD-Key
3) Whenever you connect to the DLS, the systems check that you have a registered copy of Trainz. This is carried out by using your username ("Stew2000") plus your password to planet Auran. Normally you will enter this in the CMP (for 2006), DLH (2004) etc., so that you don't have to type it every time.
4) If you are logged into this forum, use the "profile" button at the top - this should show your profile. If you then use the "edit password" option, the full password is displayed (instaed of "******"). Cancel from this and you now know your password to enter into the CMP.
HTH,
Colin
ps - do remember that the DLS can go unavailable