ParticleSystem Assertion failed

Hey guys,I meet a problem when I add a CCParticleSystem onto the scene.

This is my code:

CCParticleSystem* BG_Sprite = CCParticleSystemQuad::particleWithFile(“start_bg.plist”);
BG_Sprite~~>retain;
BG_Sprite~~>setPosition(ccp(0,0));

But unfortunately,there is a assertion failed.

There is the Assertion information:
Assertion failed!
Program:
………cpp
Line:149

Expression: dict != 0

For information on how your program can cause an assertion failure,see the Visual C++ documentation on asserts