A function stops working with no apparent reason

I'm developing a game, here is a screenshot:

http://img697.imageshack.us/img697/4415/85906798.jpg

I have a function in my main loop called moveShip that moves the player's ship if some buttons are pressed. The trouble is, some commands began to break it recently, such as removeChild(debriefingScreen), and I have no idea why. Also, firing (spawning bullet movie clips) restores the moveShip functionality 0_o Anyone has any idea why such thing could happen, or how to fix this?

I'm sorry I'm so vague, bu开发者_StackOverflowt I don't know what info to provide about this problem.

Solved with stage.focus = stage;