Once upon a time you could add or remove NewGRFs in the middle of a game, or add it to a savegame or a scenario. But this caused many problems and corrupted games. A few years ago OpenTTD devs modified the game so that players could not automatically do this in an effort to reduce the number of bug reports and increase the quality of the game.Killersquad wrote:I have a question about the Dutch Trainset 2. I downloaded it, with some Netherland scenarios. But when I want to play a scenario I cant play with the Dutch Train set
Many scenarios developed over the years were developed without adding NewGRFs, since players could do that on their own. With the change, however, those scenarios are now incomplete. To change this, you will need to enable the Scenario Editor. There is a dedicated discussion topic on how to do this here: http://www.tt-forums.net/viewtopic.php?f=29&t=53881
While adding a vehicle set shouldn't cause an issue, just be warned (as you will be when you enable this feature and start a game with it) that any changes to a scenario once it is initially saved MAY cause issues, anywhere from incorrect display of graphics or wrong prices to complete corruption of the game making it unplayable.