Predis Class '\Predis\Commands\StringSetExpire' not found

I have a very odd predis error:

Class '\Predis\Commands\StringSetExpire' not found in <b>/Users/charlie/Sites/Admin/predis/lib/Predis/Profiles/ServerProfile.php</b>

It happens when I try to use the following code:

setex($this->get_cache_key(), (60 * 60 * 24 * 30), $serialized);

The file exists. I change 开发者_JS百科directory to that exact location and I open a valid file. So, I feel that my paths are correct. I am trying to use an AJAX command to set the key, value in the redis database. What's weird is when I execute the php file from the terminal using "php filename", it doesn't throw an error at all.