Ronald,
It's not obvious that you have CurrMast currently selected. The fact that you are using RECNO("CurrMast") and FOUND("CurrMast") even suggests it isn't. I'd either change the code to:

lnRecNo = RECNO("CurrMast")
GO TOP IN CurrMast
SET EXACT OFF
=SEEK(UPPER(ALLTRIM(THISFORM.txtCurrID.Value)), "CurrMast")
SET EXACT ON

IF NOT FOUND("CurrMast")
GO lnRecNo IN CurrMast
MsgBox("Currency was not found.",,,16)
RETURN .F.
ENDIF

OR:

SELECT CurrMast
lnRecNo = RECNO()
GO TOP
SET EXACT OFF
SEEK UPPER(ALLTRIM(THISFORM.txtCurrID.Value))
SET EXACT ON

IF NOT FOUND()
GO lnRecNo
MsgBox("Currency was not found.",,,16)
RETURN .F.
ENDIF

Rick