what does it mean when a field is "not unique and must be qualified? example....

select bundle,length,grade,siz,shipdataid;
from data1,data2,data3,data4,data5,data6,data7,data8;
where data1.shipdataid = data2.shipdataid;
and data2.shipdataid = data3.shipdataid;
and data3.shipdataid = data4.shipdataid;
and data4.shipdataid = data5.shipdataid;
and data5.shipdataid = data6.shipdataid;
and data6.shipdataid = data7.shipdataid;
and data7.shipdataid = data8.shipdataid;
and data8.shipdataid = data1.shipdataid;
and grade = gdValue and siz = szValue and length = 2 ;
into cursor myCursor


I've got a nasty report to create, and (ha,ha) I'm trying to teach myself how to use cursors.