file_get_contents works in base script but not in an included script

In PHP4, I am using file_get_contents('file.sql',true) to bring in SQL queries from files who's directory is on the include path. It works fine in the main php scripts (ones accessible through URLs), but when done in a php script that is included by one of the main scripts I just get false instead of a string. The files exist, the include path is correctly set at all times (I've checked), and the exact same code works when placed directly in the main php script. I've been tearing through documentation for hours. Is there some quirk, or setting I'm missing? Below is an example of what I'm doing. main.php <?php set_include_path(get_include_path . ':/absolute/path/to/sql'); include('inc.php'); $SQL1 = file_get_contents('query.sql',true); //$SQL1 == contents of query.sql ?> includes/inc.php <?php $SQL2 = file_get_contents('query.sql',true); //$SQL2 == false //My path is still intact here ?>