I´m using C-Script.
I read that it doesn´t matter whether u use the upper or lower case or both.
I get the script from... I don´t know, it´s long ago I think...
I used it often in projects and there was never a problem like this. Except when I tried to change the Level and change then back, the script was faulty.
If theres a better Script for changing Levels, someone could post it.
Ah, the problem report,

//Script of Level 1:

action Level_2
{
while(vec_dist(player.x,my.x)>100)
{
wait(1);
}
msg_show("",5);
wait(2);
LEVEL_load("Level_2.wmb");
}

//Script of Level 2:

action Level_3
{
while(vec_dist(player.x,my.x)>100)
{
wait(1);
}
msg_show("",5);
wait(2);
LEVEL_load("Level_3.wmb");
}

While changing from Level 1 to Level 2:
Problem report:

<Level_3> Action not found.