Problem solved... I forgot to remove the column_left.php wich I don't use (I print the category in the header) and that was declaring 2 times tep_show_category().
Now I've a doubt... I have a tax applied to cash on delivery method but the "calculate total" button of this contribution doesn't check if payment method is cod, transfer,etc or doesn't apply correctly the tax if is needed. How could I add the tax of COD method to the "total box" printed in this contribution ?