i have a problem with polymorphic lookup when trying to remove a table from it using polymorphic lookup manager in xrmtoolbox i got the following error relation ship cannot be deleted since it is not a custom entity relationship
the relationship is between PhoneCall that is a system table and applicant interview that is a custom table
also when trying to delete the relationship from the solution from the side of PhoneCall table or Applicant Interview Table i got the same error Entity Relationship: cr884_applicantinterview_PhoneCalls Cannot be deleted since it is not a custom entity relationship
the following picture is from xrm toolbox