curency conversion in crystal report

hi friends iam using towards function in crystal reports for to display the 150000
" one lakh fiftythousend rupees only"

iam using bellow formula but it shows A number,currency amount, boolean, date,time, or string is expected here..

numbervar RmVal:=0;
numbervar Amt:=0;
numbervar pAmt:=0;
stringvar InWords :="Rupees ";
Amt := tonumber({@net_sal});
if Amt = 10000000 then RmVal := truncate(Amt/10000000);
if Amt = 10000000 then RmVal := 1;
if RmVal = 1 then
InWords := InWords + " " + towords(RmVal,0) + " crore"
else
if RmVal = 1 then InWords := InWords + " " + towords(RmVal,0) + " crores";

Amt := Amt – Rmval * 10000000;
if Amt = 100000 then RmVal := truncate(Amt/100000);
if Amt = 100000 then RmVal := 1;
if RmVal =1 then
InWords := InWords + " " + towords(RmVal,0) + " lakhs";

Amt := Amt – Rmval * 100000;
if Amt = 0 then InWords := InWords + " " + towords(truncate(Amt),0);
pAmt := (Amt – truncate(Amt)) * 100;
if pAmt = 0 then
InWords := InWords + " and " + towords(pAmt,0) + " paisa only"
else
InWords := InWords + " only";
UPPERCASE(InWords)