>>>Hi everybody,
>>>
>>>I added NODEFAULT and return in Checkbox Click event, but it still changes the value.
>>>
>>>How can I prevent it?
>>>
>>>Thanks in advance.
>>
>>Set it to ReadOnly or Enabled = false
>
>Unfortunately, When event now prevents the Click from executing even if I return true. Could it be because I'm calling Messagebox and it "eats" the click?

Certainly possible.

Why don't you just use Value_assign to keep the Value from changing?

-m.