After upgrade to 4.6.0 (Drupal 7.36) problem with Add Contacts to Event action

[jonathankissam]

After upgrading a clients' site to 4.6.0, I am getting this error when I try to use "Add Contacts to Event" to register multiple contacts for an event:

Warning: Variable passed to each() is not an array or object in CRM_Event_Form_Participant->postProcess() (line 904 of/home/vtmfspor/public_html/sites/all/modules/civicrm/CRM/Event/Form/Participant.php)

$this->_contactIds is empty when the postProcess method is being called.

I can batch update participant records via profile - just can't add contacts to the event in the first place.

Screenshots are attached.  Thanks for any help.