He everyone

I have very strange and big problem with my last V from edius 4.6, when I make two
video track and make dissolve between it I had red line for rending and playback is stop it and need rending my work , I know you will ask about my power of the PC but I will tell you that happen for almost very fast PC in our local broadcast here as this problem wasn’t existent in our old V like pro 3 and 4, its only existent in the last virgin , any one have experience 4 that?