I did it. That error disappeared, but there are another errors: syntax error in this line: VECTOR Wind_direction= 0,0,-30 ;
I changed the line to VECTOR wind_direction; and the big error comes here:
vec_set(my.vel_x,vector(Wind_direction.x,Wind_direction.y,Wind_direction.z));
error: vel_x is not member of 'ENTITY'