>visible=.t.
>The problem not resolved.

Yes but that doesn't help me to understand the problem. How to reproduce it?

PS:

Public oForm
oForm = Createobject('myForm')
oForm.Show

Define Class myForm As Form
  DataSession = 2
  Height=300
  Width=300

  Add Object myButton As CommandButton With Caption="Mark All"
  Add Object myGrid As Grid With Width=300,Height=200,Top=50

  Procedure Load
    Create Cursor test (myLogical l, myValue c(10))
    For ix=1 To 100
      Insert Into test Values (Int(Rand()*100)%2 = 0, Sys(2015))
    Endfor
    Locate
  Endproc

  Procedure Init
    With This.myGrid.Columns(1)
      .AddObject("mycheck","CheckBox")
      .CurrentControl = "myCheck"
      .Sparse=.F.
      .myCheck.Caption = ''
      .myCheck.Visible = .T.
    Endwith
  EndProc
  
  Procedure myButton.Click
  Update (thisform.myGrid.Recordsource) set myLogical= .t.
  thisform.myGrid.Refresh()
endproc
Enddefine

Cetin