customising bradabra

Hi! I am trying to use the forceforge project functions! I have n fields for Sum on rows and js-function for calculating Total in my php function:
echo "
<script language='javascript'>
function CalcAllTotals (obj_DestForm)
{
var i;

// compute totals for each references
for(i=0 ; i<".$txt_n_entries." ; i++)
{
var obj_Quantity = eval('obj_DestForm.txt_q_' + i);
var obj_UnitPrice = eval('obj_DestForm.txt_up_' + i);
var obj_Currency1 = eval('obj_DestForm.txt_totCurr1_' + i);

CalcRefTotals(obj_Quantity, obj_UnitPrice, obj_Currency1);
}

// compute last ones
CalcTotalHT(obj_DestForm, obj_DestForm.txt_totHT_curr1);
CalcVAT(obj_DestForm, obj_DestForm.txt_vat_curr1);
CalcTotalTTC(obj_DestForm, obj_DestForm.txt_tot_curr1);
}
</script>";

Any suggestion how to make this work? It is complaining "Object required" on line with "var obj_Quantity".
Many thanks
D.