taxonomy.selectNodes error in Flash

I hope I'm asking this is the right place (long time listener, first time caller) -

I'm calling the taxonomy.selectNodes from inside a Flash movie, and I keep getting an error from the taxonomy.module: Invalid argument supplied for foreach() 1086 .
I've made calls using the node.get and views.get with wonderful results. Also when I use the call method in the services module page for taxonomy.selectNodes, I get the information I need. So my guess is I'm just writing this call wrong:
drupal.call( "taxonomy.selectNodes", new Responder( listNodes, onError), sessionId, 1 );

Any ideas?
I'm able to get the same information I need using the views.get, but this is such a wonderful module I'd like to use it for its full potential.
Thanks