Is it Carnation Coconut Milk in the recipe or have you subbed it? The super low fat content of the Carnation stuff mans that the milk proteins are not protected and that means you are more likely to get curdling. By heating the milk first, the protein will have a chance to bind first before you add the thing that will cause the curdling, itms, so bring the milk to temp first next time, and add the lime juice at the end, it may help.