Hello Leo,
When you reinstall the game, you need to enter exactly the same license info you entered the first time you installed the game, otherwise you get an error message.
By default, when registering, license info are proposed to be saved in "my documents" folder, file "NSR_LicenceInfo.htm".
If you've lost your license name, you can go on this page :
https://shop.nitrostuntracing.fr/licens ... anguage=en
We can't get your password, since we don't store them in clear, so if you've lost it, you can go on this page to get a new one :
https://shop.nitrostuntracing.fr/passwo ... anguage=en
And finally, to get your license info and profile codes, you can go on this page :
https://shop.nitrostuntracing.fr/licens ... anguage=en
Hope this will help to solve your problem. If you enter the correct License Name and password, it should work.