Incorrect key file for table try to repair it error

When i get data by SQL query using phpmyadmin database table but i received error "#126 - Incorrect key file for table '/tmp/#sql_1e8b_3.MYI'; try to repair it" I searched about it. But i can't solved it. I change tmpdir using my.cnf file that place into etc folder. So, my.inf file located at etc/my.cnf and then after restart mysql using cpanel >> Home " Restart Services " SQL Server (MySQL) But it is not solve. Please help me.