visa for americans in austria

i am an american who lives in austria.My wife is austrian.I have an unlimited residence permit for austria.I have been visiting china many times to go to trade shows.I have arranged over 100 containers to be shipped to europe and america.I have never required a letter of invitation,but my last one was given me me with only 2 entries.this causes me trouble because from the canton fair i need to go to the hongkong fair and back to canton and shanghai and back to hongkong to fly to europe from hongkong