My script is making my movie clip to run slow

Hi there.
While trying a new way to do things. I got a message -quite ugly- saying that “my script was making my movie clip to run slow and that might affect my computer and bla bla bla”

I have to create 19000 little squares. I tried first by creating one by one but at number mc_b_3000 i got more then tired and decided to look for a better way.
I know that i have a quite “small” loop, but how could i avoid the ugly message when my users see the movie?

here is the code:

for (i = 1; i < 19001; i++) 
   duplicateMovieClip(mc_b_e, "mc_b_g_" + i, _root.getNextHighestDepth());
   j =0;
   p_x = 31;
   p_y = 99;
   while ( j < 201) 
    if(i == 95) 
     p_y= p_y+10;
     p_x =31;
    p_x = p_x+10;
    _root["mc_b_g_" + p]._x = p_x;
    _root["mc_b_g_" + p]._y = p_y;