Object has overlapping UVs. Make sure that you use a correct lightmap/2nd uv channel with non overlapping uv’s. Here you can read about it:
Object has overlapping UVs Dear : Many thanks for helping me. I have read all the links you sent me. It has a very good content. I understood what you said me. When I built one mesh in a program like Maya or 3DS containing two UV maps, I may have some problems. What I do not ...