I too tried earlier with POWL and was not able to figure it out in the given short duration, so I had disabled the toolbar button option which used to trigger OBN.
In my current project I have similar situation where some of the OBN links working and some giving error. I too need to fix it. Next week I will try and will update you. Some how the 7.3/7.4 portal, the OBN properties dosen't sow up properly in iView.