CRM Bulk Edit : Account Name lookup field disabled

Hello,

I'm trying to bulk update my contacts to set their account name field, however, I find this lookup field disabled in the bulk edit form. I understand that this happens when there is an enabled event on the lookup field. I checked the Contact form and found that there are no events associated with that field. 

How can I know which event is causing that field to be disabled? 

And no event associate to it: 

Thanks, 

SB