The “Undefined wp_die()” WordPress MU Installation Error

Once when installing WordPress MU, after submitting the form in the setup wizard, I got the following error:

Fatal error: Call to undefined function: wp_die()

I did extensive research a la Google, and lots of other people seemed to have the problem [1, 2, 3], but I still couldn’t find the answer.

I finally figured it out: the database user I had added wasn’t setup with permissions to access the database. Apparently there’s a bug in WordPress MU that chokes on this instead of displaying an explanatory error message.

If that trick doesn’t work, I’d suggest double-checking your database information. In particular, if you’re in a shared hosting environment, you’ll probably have to prefix the database name/user with some form of your hosting username (e.g. “username_database” instead of just “database”).

Hope this helps someone!