How to use an unbound checkbox for multi selection in a continuous form

Actually I have one main form when one of the button of this form is clicked it open modal  continous form where i have one unbound checkbox.When this checkbox is checked i need to assign value of one of the textbox of main form to textbox of the subform.
I am able to grab the value of main form textbox value to one of the variable defined in the subform.But i am unable to do the task of assign the value of that variable to textbox of subform when unbound checkbox is checked.Here is some code which i try by creating the transparent command button named Command39   :

Public Profile_ID As Integer(Note:this is the variable which contain value of textbox  of main form)
Dim colCheckbox As New Collection

Public Function IsChecked(vID As Variant) As Boolean
   Dim lngID      As Long
   IsChecked = False
   On Error GoTo exit1
   lngID = colCheckbox(CStr(vID))
   If lngID <> 0 Then
      IsChecked = True
   End If
exit1:
End Function

Private Sub Command39_Click()
On Error GoTo Err_Command39_Click

 If IsChecked(Me.ProfileID) = False Then
      colCheckbox.Add CLng(Me.ProfileID), CStr(Me.ProfileID)
   Else
      colCheckbox.Remove (CStr(Me.ProfileID))
   End If
   Me.chkbox_AssociatedImage.Requery

Exit_Command39_Click:
    Exit Sub

Err_Command39_Click:
    MsgBox Err.DESCRIPTION
    Resume Exit_Command39_Click
   
End Sub

In above code name of checkbox is chkbox_AssociatedImage and  ProfileID is name of textbox of the subform where value need to be assign when chekbox is checked.And on last thing i used control source of checkbox like this: =IsChecked([ProfileID])

SO can anybody help me by suggesting what is wrong with my aprroach.I will really happy if somebody provide me solution of my problem.

Thank you