Thank's to all for the tips you gave me yesterday.

Let me first remind you of what I was trying to solve the problem for.
I have a form in witch I have a field that can have a value of "Y" or "N" only. In the next field's WhenEvent , I want to test for the content of the first field . If the first field contains "Y" then I enable this field otherwise I dont.

But now I have a new problem. I the user changes is mind an decides to go back to field on and change its content to the other possible value then it does not work.

Here is what I tried , but this time I get an unknown member error.
The error happens in the LostFocusEvent.

First field , LostFocusEvent :

if this.value = "Y"
This.parent.second_Field.enabled = .t.
else
This.parent.second_Field.enabled = .f.
endif

Second Field , WhenEvent :

If this.Parent.First_field.value = "Y"
This.value = table.second_field
else
This.value = ""
endif