How is posicion declared? In prior versions AFAIK declared variables have been initialized to zero automatically but this does not happen nowadays.
This means you have to do it yourself, otherwise they get displaced all over your virtual world:

tamano_x = file_var_read(file_handle); //tamaño X del mapa en la primera linea
tamano_y = file_var_read(file_handle); // Tamaño Y del mapa en la segunda linea
loaddividido /= tamano_y;
file_str_read(file_handle,dat); //tercera linea se copia a el string dat
posicion.x = 0;
posicion.y = 0;
while(tamano_y > lectura_y){
...

Use the debug panel to check the amout of entities if they are created at all.