What could be causing the "Internal Server Error" message when trying to upload a file using PHP?

The "Internal Server Error" message when trying to upload a file using PHP could be caused by various issues such as incorrect file permissions, exceeding server limits, or a syntax error in the PHP code. To solve this issue, you can try increasing the upload_max_filesize and post_max_size values in the php.ini file, checking the file permissions, and ensuring that there are no syntax errors in the PHP code.

ini_set('upload_max_filesize', '20M');
ini_set('post_max_size', '20M');