Well, first off, this line of code, should probably be set up like this:
_____________________________________________________________________________________________________

if (changeto_level == 1)
{
changeto_level = 0;
level_load("level1.wmb");
}

if (changeto_level == 1)
{
level_load("level1.wmb");
changeto_level = 0;
}

_____________________________________________________________________________________________________

Second, after your script loads the level, it hasnt finished the script (which was running in the last level) so its going to try and finish it from the last map, and if it cant find the play from the last map, its going to give you an error... I think...