I upgraded the blog today to WordPress 2.5.1 The upgrade process is really simple, you just copy the new files to the server overwriting the old files and then running wp-admin/upgrade.php. At least this should have been the ideal upgrade path. But when i finished the upgrade the server threw at me an Internal Server Error page and i couldn’t do anything. The solution for this problem is to delete the .htaccess file and then open the blog administration and update the permalinks settings (be sure to set it as it was in previous installation). After you update these settings, a new .htaccess is created and things work ok from this point.