Spike,
Terribly sorry for the delayed response. I believe you know we're usually pretty good at response time, and just missed this one.
I am glad to see you got it going. If you are still having issues, definitely let us know. Common issues that can cause problems are navigating to your site in www and non-www. One may work, the other shouldn't. I think we've already fixed issues like that with your Facebook integration efforts, but worth testing again. Beyond that, it could be either caching or simply a delay in LinkedIn between your application creation and being able to use it. In general, changes in your LinkedIn application propagate slower than changes in Facebook. Not days or anything, but not always minutes, like with Facebook.
Either way, as always, definitely let us know if you run into any other issues or have other questions! We're very happy you decided to resubscribe and choose to go with both extensions!
Thanks,
Alex