We sell via partners.  I am trying to associate Leads, Accounts and Potentials with the partner that owns them.  The Lead Name or Account Name in the record represents the end customer, and I have added a custom field called "Partner" that is a Lookup field using Account Name in Accounts. 

My problem is that clicking on the "lookup" symbol now produces no response, including where it is used as a standard field (e.g. in the form to add a New Contact).   Would appreciate any suggestions on how to get it working or alternate ways to handle identifying which partner owns which opportunities.