Adding some details.
$max_upload = $this->_sizeToKB(ini_get('upload_max_filesize'));
$max_post = $this->_sizeToKB(ini_get('post_max_size'));
$memory_limit = $this->_sizeToKB(ini_get('memory_limit'));
$upload_mb = min($max_upload, $max_post, $memory_limit);
if($maxSizeKb > $upload_mb) {
$status = 'warning';
$maxSizeKb = $upload_mb;
// flash message text warning
$error .= sprintf(_m("You cannot set a maximum file size higher than the one allowed in the PHP configuration: <b>%d KB</b>"), $upload_mb);
}
$iUpdated += osc_set_preference('maxSizeKb', $maxSizeKb);
Means one of limits should be lower than your value.
You can also set this value on database