Upgrade from 3.5.2 to 3.6: Unable to locate WordPress Root directory.

I’ve set WP_DEBUG to true on wp-config.php and tried to upgrade again.

The following message repeated several times:

PHP Notice: Undefined variable: b in E:\Home\<host_username>\Web\wordpress\wp-admin\includes\class-wp-filesystem-ftpext.php on line 334

PHP Notice: Undefined variable: b in E:\Home\<host_username>\Web\wordpress\wp-admin\includes\class-wp-filesystem-ftpext.php on line 337

Do a manual reinstall via FTP and see if that works.

And of course disable plugins (rename the folder) to see if that fixes it if not.

The blog in question only has Akismet 2.5.8 active. Jetpack 2.3.3 is there, but it’s not active. It’s a new blog, started from WP 3.5.2. So definitely plugins must not be the cause of the problem.

And of course I know that a manual upgrade over FTP fixes it. But I want to solve the issue of not being able to upgrade WordPress and install/upgrade plugins from its own admin. My point is I want this WP tool working.

Edit:

I’ve checked the wp-admin\includes\file class-wp-filesystem-ftpext.php to see what might be wrong on lines 334 and 337. Below is the code from line 334 to 338:

if ( $b['islink'] )
$b['name'] = preg_replace( '/(\s*->\s*.*)$/', '', $b['name'] );

return &b;
}