In your other question (Table Links and Sums in Scripts, Create new field.) you have this expression inside a SQL SELECT. Maybe this is the problem? Any calculation inside a SELECT statement is executed by the ODBC driver and not by QlikView, and there could be limitations e.g. integers that cannot be divided to form new non-integer numbers.

Try a Preceding Load instead:

Load *,

     "estrc-cost"/"estrc-weight-qty" as unit

     ;

SQL SELECT ... FROM ... ;

HIC