Upgrade to 3.4 error: Call to undefined function get_option()

Question

After running the automated upgrade to 3.4, I receive the message

Fatal error: Call to undefined function get_option() in /.../wp-admin/admin.php on line 32

I have renamed plugins/ to plugins2/, renamed themes/ to themes2/, created themes/ and placed twentyten in there.

Still fails with same error.

I have downloaded a copy of 3.4, and uploaded /wp-admin and /wp-includes.

Still fails with the same error.

When I try to run wp-admin/upgrade.php I receive:

"Fatal error: Call to undefined function timer_start() in /.../wp-admin/upgrade.php on line 20"

Line 32 of /wp-admin/admin.php is:

if ( get_option('db_upgraded') ) {

I tried manually inserting this option set to true in the wp_options table in phpmyadmin, but the same error remains.

Answer 1

The problem was caused by about 8 wordpress files in the root directory with a filesize of 0 bytes.

Uploading fresh copies of these files (from the latest version downloaded from wordpress.org) solved the initial problem.

The subsequent problem has since cleared without any indication of what steps solved it.