I has this issue but for other reason. I was upgrading from and early version to 2.6.2. The first thing is reading the upgrade log in the main directory… there´s a error_log file on the root of the website.
I got a problem with the latin1 charset of the database, the upgrade script doesn´t recognice the collate and gives and error, then the new tables of this version don´t get created.
The fix: comment the lines that refer to latin1 in wp-config.php and redo the upgrade process. All works fine then.
