Why dose the application crash at cloth1->removeCollisionCapsule( 1 )

I use the Physx-3.3 and the cloth1 is a PxCloth*
Why dose the application crash at cloth1->removeCollisionCapsule( 1 )
(T_T)

cloth1->addCollisionSphere( PxClothCollisionSphere( PxVec3(2.0f, 0.0f, 0.0f), 1.0f ) );
	cloth1->addCollisionSphere( PxClothCollisionSphere( PxVec3(0.0f, 2.0f, 0.0f), 1.0f ) );
	cloth1->addCollisionSphere( PxClothCollisionSphere( PxVec3(-2.0f, 0.0f, 0.0f), 1.0f ) );
	cloth1->addCollisionSphere( PxClothCollisionSphere( PxVec3(0.0f, -2.0f, 0.0f), 1.0f ) );

	cloth1->addCollisionCapsule( 0, 1 );
	cloth1->addCollisionCapsule( 1, 2 );
	cloth1->addCollisionCapsule( 2, 3 );
	cloth1->addCollisionCapsule( 3, 1 );

	cloth1->removeCollisionCapsule( 1 );