What are some common reasons for the "Failed opening required 'DB.php'" fatal error in PHP?

The "Failed opening required 'DB.php'" fatal error in PHP typically occurs when the script is unable to locate or include the required file 'DB.php'. This could be due to incorrect file path, missing file, or file permission issues. To solve this error, ensure that the file path is correct and the file 'DB.php' exists in the specified location.

// Correcting the file path to include 'DB.php'
require_once('path/to/DB.php');