If you have turned on conditional gets on a curl handle, and then for a subsequent request, you don't have a good setting for CURLOPT_TIMEVALUE , you can disable If-Modified-Since checking with:
<?php
$ch = curl_init();
curl_setopt($ch, CURLOPT_URL, $foo);
curl_setopt($ch, CURLOPT_TIMEVALUE, filemtime($foo_path));
curl_setopt($ch, CURLOPT_TIMECONDITION, CURLOPT_TIMECOND_IFMODIFIEDSINCE);
curl_exec($ch);
curl_setopt($ch, CURLOPT_URL, $bar);
curl_setopt($ch, CURLOPT_TIMEVALUE, null); curl_setopt($ch, CURLOPT_TIMECONDITION, 0); curl_exec($ch);
?>
