Hello,
thanks for the answers but is not working with all the plugins disabled and changing the version to "1.8.2".
I think can be related to the collation of the database, all my tables and the database are defined to latin1_swedish_ci, i don not why, my web is in spanish, but works fine. I will try changing the collation of the database before the upgrade and i think i will have to check the database schema, perhaps in a earlier upgrade some tables could be left in an worng/obsolete state...