Cusco, the EUREL.NBI file is a 62Mb monster, and will therefore be the terrain database itself, I suppose.
First thing I'd do would be to uninstall the program from your hard drive and then re-install, and see if that fixes it. If not, request a replacemnt CD from Navbox. My experience with their support email is that it's quick and fair, so good luck.
I haven't got my CD with me, but another option might be to see if the EUREL.NBI file is visible when looking at a file list of the CD. If so, the solution may be as simple as copying it across to the PP50 directory on your hard drive.
Jepp, I remain at a loss to understand your concerns. The items you mentioned having experience of are minor niggles at best. Cusco's problem is rather more serious, but does not seem to be representative of user's experience based on chats here and elsewhere (completely unscientific, I know). MY guess is that his difficulty is an anomaly, either in the instal process or on his particular CD copy.
I really hope your Username doesn't reflect a vested interest, as that would be a great shame.