eaccelerator_cache_page and ob_get_contents

My code:

ob_start();
if (!isset($_SESSION['userid'])) {
$cachetimeout=10;
eaccelerator_cache_page($_SERVER['PHP_SELF'].'?GET='.serialize($_GET), $cachetimeout);
} else {
$cachetimeout=-1;
}
$output = ob_get_contents());
ob_end_clean();

ob_start();
print $output;
ob_end_flush();

Output:
??????í<Û’Û¶’y©Ú@äZ{\‰Ä;©{j$ÍØg×ö¦'[¶K‰È/ ÎxrœØ?ت­}Ü·}:¯Ù9² €¤H]ƍ윜â\$lt7îv÷ËÑ¿ Çÿþír¨ï¡oÿÚk!`͏{9¯B/<Â.9Y¨Œ·c¼x…}d\FãdFèÌíÉäv9²†G‚u üÕWŒÊɉ;Gggî?«O¿™c/&m%DÜ9á-Þ¸ï3Ç1CüU¯†BÛ®
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ø» É5 è)ümv˜KìŒ÷ö„w÷k†„ÍxXãž6¢ðfû¢¾D}Õãx¾AOØ÷Ô†ÆËÆ‹ ð%| Îv°Å%ìÚ9o´¨Gk
`€‹ úRîç•Âv%a)N»Óоe߶{\»W»YÖú'yi

Help me!