Low framerate problem.

[oolblue]

button.tweener.delay = 0.04f;
button.tweener.duration = 0.04f;
button.tweener.PlayForward();

this code is no problem in high framerate (at least 30fps).
but if framerate under 20fps, button is not appear (both game-view and scene-view).
I modify button's position in game running (little bit), suddenly it is appear.
i have many time debugging, i cannot found any problem in my code.
what is problem?

my unity version is 4.5.0f6, and ngui is 3.7.2.

[ArenMook]

Let me guess... scaling from scale of 0? Zero is invalid scale.