[AccessD] IsDirty

I am having problems on the close button of my form. I want to make sure
certain fields are completed before they close the form. I am trying to use
IsDirty so the form closes if there hasn't been any changes made and also if
all the fields have been completed. I am using the below code and receive
the error, object not supported. This is a form/subform and the close button
is on the subform. If I remove the IsDirty, it works.

 

 

 If Forms!frmEvalMain.frmEvalSub.Dirty = True Then    'Data Entered?  Yes
    If Len(TypeID & "") = 0 Then
       MsgBox "You must enter a Type." & vbCrLf, vbCritical, " Entry
Required"
       TypeID.SetFocus
    ElseIf Len(Title & "") = 0 Then
      MsgBox "A title must be entered." & vbCrLf, vbCritical, " Entry
Required"
      Title.SetFocus
    ElseIf Len(Author & "") = 0 Then
       MsgBox "An Author must be entered." & vbCrLf, vbCritical, " Entry
Required"
       Author.SetFocus
        Else
         
         response = MsgBox("Do you want to Exit?", vbYesNo + vbQuestion,
"Exit")
         If response = vbNo Then
           Title.SetFocus
         Else
             DoCmd.RunCommand acCmdSaveRecord
            DoCmd.Close acForm, "frmEvalMain"
         End If
      End If 

 Else
   DoCmd.Close acForm, "frmEvalMain"
 End If

 

Virginia