Problems:
1. my_function(); not my_function;
2. Maybe use {} brackets...
3. Move_left() moved character right.
So, entire corrected code:
Code:

---

//////////////////////////////////////////////////////////////////////////
#include <acknex.h>
#include <default.c>
//////////////////////////////////////////////////////////////////////////

var sprite_stand_frames = 6; // Spriteanzahl fur Standani

var counter = 0; // Startframe

//////////////////////////////////////////////////////////////////////////

PANEL* hero =
{
	//bmap = "Alucard_stand.tga";
	window (320,240,24,48,"Alucard_stand.tga",counter,0);
	flags = VISIBLE;
}

PANEL* wertausgabe =
{
	digits ( 10,10,10,*,1,counter);
	flags = VISIBLE;
}

//////////////////////////////////////////////////////////////////////////

function move_right()
{
	hero.pos_x += 2;
	wait(1);
}

function move_left()
{
	hero.pos_x -= 2;
	wait(1);
}

function move_stand()
{
	while(1)
	{
		if (counter >= (24 * sprite_stand_frames))
		{
		  counter = 0;
		}  
		else
		{
		  counter += 24;
		}  
		
		wait(60);
	}
}

//////////////////////////////////////////////////////////////////////////

function main()
{
	fps_max = 60;
	video_mode = 7;
	screen_color.blue = 150;
	wait(-1);
	
	while(1)
	{
		if (key_d == 1) {move_right();}
		if (key_a == 1) {move_left();}
		if (key_a == 0 && key_d == 0) {move_stand();}
		wait(1);
   }
}

---