I have tried tracing the methods but everthing seem fine

this the code where the problem arises which is from tastrade grid class which I have used with only one minor change for evaluating the order for calculation.
******************
IF EMPTY(this.cFieldToSum)
RETURN
ENDIF

LOCAL lnOldArea, ;
lnOldRecNo, ;
luKey, ;
lcFieldToSum, ;
lcOrder,;
lstalk


lnOldArea = SELECT()
this.nColumnSum = 0
lcFieldToSum = ""

IF EMPTY(this.RecordSource)
RETURN
ENDIF

*-- Select the alias specified in the grid's RecordSource property
SELECT (this.RecordSource)

lcOrder = ORDER()
luKey = IIF(!EMPTY(lcOrder), EVAL(key(tagno())), "")
lnOldRecNo = IIF(EOF(), 0, RECNO())
lcFieldToSum = this.cFieldToSum

lstalk = set('talk')
set talk off
*-- Total up the column and store the result
*-- in the nColumnSum property
IF !EMPTY(lcOrder) AND SEEK(luKey)
SUM &lcFieldToSum. ;
WHILE luKey = EVAL(key(tagno())) ;
TO this.nColumnSum
ELSE
IF CURSORGETPROP("SOURCETYPE") = DB_SRCLOCALVIEW OR ;
CURSORGETPROP("SOURCETYPE") = DB_SRCREMOTEVIEW
*-- Grid is bound to a view
SUM &lcFieldToSum. ;
TO this.nColumnSum
ENDIF
ENDIF

IF lnOldRecNo <> 0
GO lnOldRecNo **********Error Occurs Here**********
ENDIF

SELECT (lnOldArea)
if lstalk = 'ON'
set talk on
endif
***********

Rajesh