No OAuth context found

I get 500 Internal Server Error: An error occurred (0): No OAuth context found when trying to make a 2 legged OAuth connection to a test service. Everything I could find by search says this is already fixed. I'm just trying to get a single user to test out Services. Here's my simple test code I'm running:

$oauth=new OAuth($key, $secret);
$oauth->enableDebug();
$oauth->fetch($url);

I'm wide open to the possibility I just configured something wrong, but damned if I can find it.