This kind same error we get normally whenever there same statement has executed at a time on same table or this table given task recently got completed.
even when you grating the table, if grant all ready exist gets same error.
hive>grant select on table database.tablename to role role1with grant option;
FAILED: Execution Error, return code 1 from org.apache.hadoop.hive.ql.exec.DDLTask. Error granting privileges: null
It's better to ignore and proceeds with next task.