You may set the InputMask of that TextBox to "Y" it allows to user to input ONLY "Y","N", "y", "n". If You want to validate the record put the check of the whole form in some separate method i.e. thisform.AllOK(). In QueryUnload event of the form put:

IF .NOT. ThisForm.AllOk()
   NODEFAULT
   RETURN .f.
ENDIF

In Close button (set its propertie Cancel to .t. so If the user press ESC to its Click Event ot be fired) just set

thisform.Release() && that will not fire QueryUnload Event of the from

Anywhere else You have thiform.Release) You must change that line to:

IF thisform.QueryUnload()
   thisform.Release()
ENDIF