Before Update Save Fails

Hi, i am trying to perform a beforeupdate event on a record, but seem to be getting an error.

The undo function works fine but it cannot save, i would be grateful if someone can help as the error is unclear.

Code:

Private Sub Form_BeforeUpdate(Cancel As Integer)

If MsgBox("Are you sure you want save these changes?", vbQuestion + vbYesNo) = vbYes Then
DoCmd.DoMenuItem acFormBar, acRecordsMenu, acSaveRecord, , acMenuVer70
Else 'user clicked no
DoCmd.DoMenuItem acFormBar, acEditMenu, acUndo, , acMenuVer70
End If

End Sub



Error that i am getting.....

Run-time error '2115'

The Macro or function set to the beforeUpdate or ValidatationRule propety fot this field is preventing from saving the data in the field.

Thanks