Enable/Disable the field in continous form conditionally

Hi all,

I am using the countinous form. I want to Enable/Disable the some
fields for perticular records as per the following condition when
open the form. I have written this code in "On Current Event". I go on
the perticular record its enable/dosable the following field for all
records. I have tried this code in "On Open Even" but there is no
effect.

Please help me to solve this problem.

Private Sub Form_Current()
If (Me.Grade = 9 Or Me.Grade = 10 Or Me.Grade = 11 Or Me.Grade = 12 Or
Me.Grade = 13 _
    Or Me.Grade = 14 Or Me.Grade = 15) And Me.TotDay <= 40 Then

    Me.ManagerApproval.Enable= False
    Me.ManagerConfirmation.Enable= False
Else
    Me.ManagerApproval.Enable= True
    Me.ManagerConfirmation.Enable= True
End If
End Sub

thanks in advance.