At the risk of being branded completely useless, shouldn't it be:

define class upload as custom olepublic
     procedure openfile
     LPARAMETER cPathName
     if parameters() < 1 then
           return .f.
      else
           return "FOO"
      endif
enddef

>At the risk of boring the crap out of you, here is the complete code:
>

>DEFINE CLASS upload AS Custom OLEPUBLIC
>	PROCEDURE OpenFile(cPathName)
>		IF PARAMETERS() < 1
>		   This.LastErrorC="No file specified"
>		   RETURN .F.
>		ENDIF
>