I get the same error when creating a sales order, a few days ago worked normally.
here is the error message with go_debug = 2
This edit session has been abandoned by opening sales document in another browser tab. You cannot edit more than one sales document at once.
D:\nginx\html\frontaccount\sales\includes\sales_ui.inc:50: display_error('This edit session has been abandoned by opening sales document in another browser tab. You cannot edit more than one sales document at once.')
D:\nginx\html\frontaccount\sales\sales_order_entry.php:228: check_edit_conflicts()
running winxp, nginx 0.93 ,php5.3.4 , mysql 5.1.54