APC throws "apc_store() expects parameter 3 to be long, string given". Validates the TTL to an integer.
diff --git a/system/libraries/Cache/drivers/Cache_apc.php b/system/libraries/Cache/drivers/Cache_apc.php
index 93993d0..a3dd469 100644
--- a/system/libraries/Cache/drivers/Cache_apc.php
+++ b/system/libraries/Cache/drivers/Cache_apc.php
@@ -68,6 +68,7 @@
 	 */
 	public function save($id, $data, $ttl = 60)
 	{
+		$ttl = (int) $ttl;
 		return apc_store($id, array($data, time(), $ttl), $ttl);
 	}