Looks to me as if the problem might be with the while loop. It allows the frame 41 to be used when it does not exist. It should be:

Code:

---

{		my->frame += 1*time_step;
		if(my->frame >= 41) my->frame -= 40;
		wait(1);
}  

---

or:

Code:

---

{		my->frame += 1*time_step;
		my->frame %= 41;
	 	wait(1);
}  

---

at least that's how to use the modulo operator in c-script

cheers

edit: Also wonder why you want to tie the frame number to time_step and not the time each frame is shown. It should really be:

Code:

---

{
		my->frame += 1;
		my->frame %= 41;
	 	wait(-time_step); // multiply with 0.01 ... 100 to adjust length
	 	wait(1);
}    

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