Fatal error: Uncaught Error: Call to undefined function wp_get_network()

The error occurs because WordPress tries to call a function that does not exist in the loaded code. The core defines get_network() but the call uses wp_get_network(). The mismatch stops PHP execution and produces a fatal error.

When the function is missing, WordPress cannot load network features. The script aborts before any page output, resulting in a blank screen or error message.