In my recent answer, I argued that both of Karṇa's two unfortunate curses were interpolations i.e., they were not part of Vyāsa's original Mahābhārata. I think the reason behind those particular interpolations is to elevate the stature of Karṇa, i.e., show him on par with Arjuna and that he'd be unbeatable if not for those two curses - one from a brāhmaṇa and other from Paraśurāma.
Apparently, there's a third curse-story mentioned in various online blogs according to which Karṇa tried to squeeze out spilled ghee (clarified butter) from soil which upset Bhūdevī (Goddess of Earth), so she cursed Karṇa.
The full story from one such blog is:
Sometime later, when he was on a tour of his new kingdom, Karna is said to have encountered a girl who was crying out of fear of her step mother since her ghee had fallen to the ground. Being generous enough Karna told her that he would give her new ghee. But, the child insisted that she wanted only the ghee that was mixed with the soil and refused to take the new ghee. Taking pity on the girl, Karna took the soil mixed with ghee in his fist and squeezed it with all his might to extract the ghee and pour it back into the pot. However, Bhoomi Devi (Mother Earth) was furious at him for hurting her for the sake of a mere child. So, the Earth goddess cursed him that in a very crucial battle of his life, she would trap his chariot wheel in the same way that he held the fistful of soil, thereby making him vulnerable to his enemy.
Thus, Karna was cursed on three separate and independent occasions.
What is the origin of the above story? Which scripture contains it? Can you cite the exact verses or their translation from the relevant scripture?