>>>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
>
>No one with good suggestions of resolving the problem? It's probably a bug - but I'm not sure what workaround options are?

How about

IF (ChangeNotAllowed)
  this.Value = IIF(this.Value=0,1,0)
ENDIF

in the Click event (g)