I am using odoo etl tool which I got from odoo apps to migrate my database to 8th version.After entering the details,when I start migration process I am getting this error.Any help would be appreciated 

TransactionRollbackError: could not serialize access due to concurrent update

CONTEXT: SQL statement "SELECT 1 FROM ONLY "public"."res_users" x WHERE "id" OPERATOR(pg_catalog.=) $1 FOR KEY SHARE OF x"