Thanks for the reply, my problem shouldn't be related to the if-clause or the == mark, I tried to remove them but same error..

i define and use them in a procedure:

procedure MyProc
  LOCAL MyString

  ....
  MyString=""
  ....
endproc

>>For your reference:
>>(1) Set it to a space doesn't work too
>>(2) I also though it may because VFP dunno it's char type, so I tried
>>MyString="xxx"
>>MyString=""
>>also not work..
>
>How and where did you define those varialbes?