Maybe solved!Doc_Savage found a possible solution to this problem. As I was not able to reproduce the problem, I cannot verify if it helps.
http://www.adventuregamestudio.co.uk/yabb/index.php?topic=45945.msg617135#msg617135Hi!
Selmiak reported an error in my game:
"There was an error drawing object1. It's current sprite, 56, is invalid."

He used 2x antialiased filter. I can't reproduce it and the error did not reoccur when he restarted the game.
Another player reported the same error but with completely different screen settings (fullscreen, no filters).
Both were using Direct3D 9 (I set this as default because in direct draw mode the music stuttering happens on room change)
Additionally I have to say that all sprites use alpha channel.
There is no line number in the error message but I think this lines cause the problem:
oBowlEmpty.Visible = true;
Wait(40);
oUdder.Graphic = 56;
Wait(20);
oUdder.Graphic = 100;
Wait(20);
oUdder.Graphic = 56;
Wait(20);
oUdder.Graphic = 100;
Wait(20);
oUdder.Graphic = 55;
Any idea what this could be?
Edit: Forgot to mention - I use AGS Editor .NET (Build 3.2.1.111)
v3.2.1, March 2011