I think you may have to change the use of the quote marks:

SELECT Assets.asnum, Assets.sub, Assets.aexistnum, Assets.asdes,;
       Assets.asser, Assets.aloc, Assets.adep, Assets.price, Assets.invoice,;
       Assets.acost, Assets.Trans_sold, Locate.locphone, Locate.person, Locate.exist, Udep.desc1;
       FROM  locate, assets, udep ;
         WHERE Locate.locnum = Assets.aloc;
           AND Udep.dep = Assets.adep ;
           AND Assets.adep = madep;
           AND Assets.astyp = mastyp;
           AND Assets.aloc = mloc;
           AND (Assets.trans_sold = ' ' OR  Assets.trans_sold = 'I') ;
       ORDER BY Assets.adep, Assets.aloc, Assets.asnum

When you submit the SQL in the SQLPrepare, enclose the SQL in double-quotes -- SQLPrepare(gnHandle, "SELECT Assets....". Use Single quotes around the data values.