Fatal error: Cannot use string offset as an array in ...civicrm/CRM/Member/Import/Parser/Membership.php on line 450 Call Stack

I'm using a previous system which has organizations, memberships, and individuals all in one table. I'm separating it out by importing selected fields using civicrm's import functions, and was successful in importing both Organizations and Individuals. However, when I try to import Memberships, I go through all the steps until the final import & get the following error:

( ! ) Fatal error: Cannot use string offset as an array in /var/www/drupal6/sites/mysite.com/modules/civicrm/CRM/Member/Import/Parser/Membership.php on line 450
Call Stack

1. Time Memory Function Location
   1 0.0001 58024 {main}

   ( ) ../index.php:0
   2 0.0478 2917012 menu_execute_active_handler( ) ../index.php:18
   3 0.0491 2924268 call_user_func_array ( ) ../menu.inc:348
   4 0.0492 2924268 civicrm_invoke( ) ../menu.inc:0
   5 0.0712 3762968 CRM_Core_Invoke::invoke( ) ../civicrm.module:315
   6 0.2033 4906308 CRM_Core_Controller->run( ) ../Invoke.php:197
   7 0.2043 4911448 HTML_QuickForm_Page->handle( ) ../Controller.php:232
   8 0.2043 4911520 HTML_QuickForm_Controller->handle( ) ../Page.php:103
   9 0.2043 4911592 CRM_Core_QuickForm_Action_Next->perform( ) ../Controller.php:203
   10 0.2043 4911664 CRM_Core_StateMachine->perform( ) ../Next.php:63
   11 0.2227 5046640 CRM_Core_Form->mainProcess( ) ../StateMachine.php:166
   12 0.2227 5046640 CRM_Member_Import_Form_Preview->postProcess( ) ../Form.php:247
   13 0.2282 5066380 CRM_Member_Import_Parser->run( ) ../Preview.php:196
   14 0.2844 7069628 CRM_Member_Import_Parser_Membership->import( ) ../Parser.php:331