I've got a testing environment set up on my work PC, and I am starting to play around with the Multisite features of WordPress.
I'm running a Windows 7 box using XAMPP 3.1.0 to run WordPress locally for developing WordPress themes and custom WordPress sites.
Today I started with a clean slate, and installed WordPress 3.5.1 into the environment. Everything runs perfectly. I then followed the instructions here: http://codex.wordpress.org/Create_A_Network
I have 2 sites set up that are sort of working on the network now. If Site A and Site B have the Twenty Twelve theme active, everything works peachy keen.
If I have Site B set to my custom theme, everything works peachy keen.
If I have Site A set to my custom theme, everything isn't peachy keen.
When I attempt to go to any of these menu pages from Site A:
My Sites > Network Admin
My Sites > Network Admin > Dashboard
My Sites > Network Admin > Sites
My Sites > Network Admin > Users
I get this error:
Fatal error: Call to undefined function get_current_screen() in C:\WP_Network\xampp\htdocs\wordpress\wp-admin\network\settings.php on line 22
The only files I've modified on Site A and Site B are the files housed in my theme's folder, so I don't really understand why there's an error on Site A and not Site B.
Anyone have any thoughts on why this might be happening?