No! I did not make any changes to seo.class.php! I guess I have to use the 2.1c recommended by Mr Duncan.
And for everybody information, after my installation, my entire Administration catalog does not show anything until I found out there are two errors in admin/catergories.php file. Missing of "(". I'm not good at all with php files and it took me quite a long time to discover this. After I added the "(" before the tep_db_..., all my catalog appear. I hope this information will helps some newbies like me. :lol:
Line : 74
'categories_seo_url' => tep_db_prepare_input($categories_seo_url_array[$language_id])),
Line : 260
'products_seo_url' => tep_db_prepare_input($HTTP_POST_VARS['products_seo_url'][$language_id]));
Thank you so much skittles for your help