当我用reshape命令转换类型时，为什么会显示下面的错误：
reshape  wide exports,i( factoryid) j( year)
(note: j = 1998 1999 2000 2001 2002 2003)
year not unique within factoryid;
there are multiple observations at the same year within factoryid.
Type "reshape error" for a listing of the problem observations.
r(9);
谢谢各位．