Okay I found one more story -
an interesting story about Karna. It is said that the whole mahabharatha took place because of Karna. Karna in his previous life was a dangerous and invincible demon called 'sahasra kunchi' which means that he is the one with 1000 armours. As usual he becomes a great inconvenience to hermits, sages and rishis. To destroy him Lord Vishnu takes the avatar of twin brothers Nar-Narayan. To kill sahasra kunchi they need to tear off his armours. It was believed that it requires the efforts of both Nar and Narayan, to get the power to tear off each armour one needs to do 1000 years penance while the other is fighting with kunchi. In that process, Nar and Narayan with their combined effort tore 999 armours. Kunchi realised that he is going to be killed and their is one more armour left. He takes refuge of Sun God who was offered to kunthi, coinciding her summoning the sun god. So to kill kunchi Nar and Narayana have to take a rebirth. So, Nar takes birth as Arjuna and Narayan as Krishna. Krishna is a blessed soul and he knew everything. Though it appears that Krishna wins war with deceipt, he knew that the balance can be done only that way. He is not against Karna or Duryodhana. Before dying krishna asks for a boon, then Karna asks him another life where he is very rich and has good son who follows pitruvakparipalana and a good wife who always follows his words. After dying Karna goes to heaven and he feels very hungry there. But he is not offered any food. When he asks for food, everyone there shows him with their index figure towards treasure like diamonds and gold. This accounts to an incident in his life as Karna. Karna in his life has given all types of 'daan' except food. Once God tested him in form of hungry and poor sage. Karna instead of getting him some food, points out with his index figure to a place where he can get food. Now Karna gets every thing in heaven except food. He requests good to give him a life to sort out this balance. So he takes rebirth as a vysya who is very rich and has a good wife and good son. In this life he always fed poor people and never let anyone go out of his home without food. Then God came in form of an Agora to test him. The vysya invites him to his home to offer some food. Agora warns him saying that he can never satisfy him. But the vysya still insists him. When agora comes home, the vysya offers shakahara to him. Agora says that he never eats shakahara and he needs mamsahara. Vysya says that he do not prepare mamsahara at his house. Agora gets angry and when he is about to leave, the vysya promises him mamsahara. He gets mamsahara from the market and offers him. Agora denies it again saying by mamsahara he means human flesh. Vysya tries to offer himself. Agora again denies it saying that he and his wife are his host and therefore he cannot eat them. The vysya then calls his son and explains him about the problem. The vysya's son suggest to offer him and does it willingly. The vysya then kills his son and offers him to the God. The God assumes his true form and makes his son alive and assures 'moksh' after this life. This way karna reaches back to heaven.
This story about Karna is commonly untold. May be true or not true,this story is somewhat convincing
This is posted on the same thread mentioned above.