RIO DE JANEIRO, Brazil, Aug 18 (Reuters) - China, the world's top soyimporter, has a quality problem with one Brazil-based shipper butcontinues to issue import permits for other shippers, a senior Chinesequarantine authority official said on Monday."China is not forbidding imports of Brazilian soybeans...there is onlyone company with whom we have a quality problem," said Wang Qinping,deputy minister of China's quarantine authority, known as the CIQ,speaking through an interpreter by phone during a visit to an industrialstandards center in Rio de Janeiro.