In a letter which can be found
here, Obama's suggested that certain trade concessions previously extended to South African agricultural produce might be ending soon (around the end of the year).
Apparently, it's all about
the health and safety standards of chicken, beef, and pork products being imported into South Africa, and the official word on this end is that it's all over minor technical quibbles that will get sorted out one way or another as soon as the veterinary experts have had their say. I know little more than that at present...