PHP is_readable returns false after odbc connection is established

Question

<?php
echo get_current_user();
$file_path = "templates\index.tpl";
$test = getcwd() . "\\".        $file_path;
echo $test."\r\n";

if(is_readable($test)) {
echo ("Readable!\r\n");
} else {
echo ("Not readable!\r\n");
}

odbc_connect("kontaktdb", null, null);
?>

Returns "Readable!"

<?php
echo get_current_user();
$file_path = "templates\index.tpl";
$test = getcwd() . "\\".        $file_path;
echo $test."\r\n";

odbc_connect("kontaktdb", null, null);

if(is_readable($test)) {
echo ("Readable!\r\n");
} else {
echo ("Not readable!\r\n");
}
?>

Returns "Not readable!"

So when is_readable is called after the ODBC Connection is made, it fails - nothing else has changed.

Windows Server 2012 + IIS + PHP 5.4.45

I have absolute no idea what's the cause of it. Any ideas?