business visa to china to attend Canton fair April 2016

am a leading business man visited china in the past for many times since 1993, and wanted to attend canton fair in guangzhou April 2016. I was invited by my suppliers in PRC participating at the canton fair and send invitation letters. But when i visited the embassy for visa the lady at the counter informed that I need a letter from local agent in PRC. plse explain me all about. Though I am sri lankan, all products are imported to USA for PRC as my business dealings are with USA business partners. Am running out of time as i plan to visit canton fair from 1st may to 5th where my concern products and manufacturers are presence on these days.
H.A.Rodrigo