Sounds like, if I am reading this right, that you have the Nav Teq DVD Road map edition on disc?

I assume you have the Mark IV DVD Sat Nav player, to check, look on home page under navigation - FAQ

Firstly

Is the disk you downloaded a 'high' edition and not a 'professional'. (professional wont work).

Is it the road map disc ie 2006-02 or 2005-01, these are edition dates, year followed by 01 or 02 (two releases a year)

If so....

have you got the operating software on the system ie V27, V26 etc if not you need to load this on first again look on the home page under Navigation for details. Make sure it is compatible with the Road map disc.

Lastly, and unlikely due to the read out you describe it may be a download or burn error on the disk or the type of disk. Though I think this only shows on the screen as insert DVD/CD or Error reading.

Also make sure you are loading it correctly by sequence, as the player is very sensitive, again follow the procedure on the home page under Navigation 'FAQ'