Sounds like the author of WP External Links didn’t realize that somebody else can user phpQuery lib. Actually phpQuery is fantastic product. I love it.
Ok. So to fix that u have manually modify WP External Links plugin because AAM does not cause this problem (I implemented check for existing class long time ago).
Find a place where in WP External Links the author include phpQuery.php and wrap it in if statement :
Also contact the author of this plugin and notify him that he is a bad boy 🙂 (I kidding)