Mysql ERROR 1005 (HY000): Can't create table 'tmp' (errno: 13)

I'm Running Mysql on ubuntu 9.10, the process of Mysql is running as root, I'm using root account when logging to Mysql, which I gave all privileges, I'm using my own db(not mysql), I can create a table, but when i try to create Temporary table i get this error:

ERROR 1005 (HY000): Can't create table 'tmp' (errno: 13)

For this query:

CREATE TEMPORARY TABLE tmp (id int);

I've plenty of space in my hard drive, all permissions are granted(also var/lib/mysql have mysql permissions).

Any idea?Thanks,Koby