antares330: It sounds like you "forgot" to give a default value to the highscore (I must assume that since you're not providing the capx of your project).
So when going to the highscore layout, you are looking for a key in the local storage. Thing is the first time a player executes your game, they don't have keys saved.
So you should somewhere have a "On item "Highscore" is missing - Set key "Highscore" value "0" and give this default value to your highscore variable as well.
Also don't forget that local storage is asynchronous.
If you only display text in your start of layout event, it's likely you don't have the read results yet in it.
Again, it all depends on your capx and would be easier to point out exactly what's going wrong in it.