Hi, I cocos2d, I am using pushScene and replaceScene to move to next scene. But, I am confused which we should use?

When I am using replaceScene in some places app is crashing and giving errors like

-[UITextView length]: unrecognized selector sent to instance 0x842a750  
 Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '*** -[UITextView length]: unrecognized selector sent to instance 0x842a750'  

But, in my program I am not passing length to UITextView. My program is in this way
In scene1 I have UITextView, and I am replacing this scene with scene2. Then

-(id)buttonPressed:(id)sender
{
    [description removeFromSuperview];  // It is the textView(description)
    CCScene *Scene = [CCScene node];
    CCLayer *Layer = [scene2 node];

    [Scene addChild:Layer];

    [[CCDirector sharedDirector] setAnimationInterval:1.0/60];
    [[CCDirector sharedDirector] replaceScene: Scene];
}  

But, when I am using pushScene in presence of replaceScene it is working good. Please clarify me which one should use in which cases ?

Thank You