i've manually changed it from phpMyAdmin.
Now i'm with Xoops 2.5.6.
Index page is not working, but others seems to be ok : i can view /user.php correctly.
all i have on index page :
0.000296 - SET SQL_BIG_SELECTS = 1
0.000303 - SELECT * FROM config WHERE (conf_modid = '0' AND conf_catid = '1') ORDER BY conf_order ASC
0.000766 - SELECT sess_data, sess_ip FROM session WHERE sess_id = '2dr88o68gko4g9mhs9h57q6fq4'
0.000816 - SELECT * FROM users WHERE uid = '7'
0.000283 - SELECT * FROM config WHERE (conf_modid = '0' AND conf_catid = '3') ORDER BY conf_order ASC
0.002482 - SELECT DISTINCT gperm_itemid FROM group_permission WHERE gperm_name = 'block_read' AND gperm_modid = 1 AND gperm_groupid IN (1,2)
0.000368 - SELECT b.* FROM newblocks b, block_module_link m WHERE m.block_id=b.bid AND b.isactive=1 AND b.visible=1 AND m.module_id IN (0,-1) AND b.bid IN (152,52,72,150,170,169,177,178,13,92,193,90,194,145,153,151,93,79,68,66,54,17,101,171,140,97,16,173,172,95,32,62,146,96,4,148,83,191,55,9,44,7,53,1,176,175,174,147,141,139,138,137,136,135,118,106,105,104,103,102,100,98,89,86,85,81,78,73,64,63,60,57,56,51,50,49,48,47,46,45,43,35,33,18,15,14,11,10,6,5,195) ORDER BY b.weight, m.block_id
0.000280 - SELECT * FROM modules WHERE dirname = 'mytube'
0.000285 - SELECT * FROM config WHERE (conf_modid = '67') ORDER BY conf_order ASC
0.000916 - SELECT lid, cid, title, vidid, screenshot, published, hits, vidsource, picurl FROM xoopstube_videos WHERE published>0 AND published<=1368217271 AND (expired=0 OR expired>1368217271) AND offline=0 ORDER BY published DESC LIMIT 0, 3
Total: 10
may this module "mytube" be the problem ?
Edit 1 : uninstalled this module : index page is perfectly working.