Changes to the Lead_main_system_library.js file throws an error during the Qualify process if the Company Name field is not present on the form.
Call stack: Mscrm.LeadCommandActions.qualifyLeadQuick -> Mscrm.LeadCommandActions.qualifyLeadAs -> Mscrm.LeadCommandActions.$7 -> Mscrm.LeadCommandActions.$3

A variable reference for the company name field is defined:
var $v_E = Xrm.Page.getAttribute("companyname");

An initial null check is performed, but later in the code a function on that variable is called without a null check:
!$v_E.getUserPrivilege().canRead

A workaround is to put the field back on the form and hide it, but this is a short-term solution and we would like to see the issue addressed.