WordPress statistics stop working on independent site

Hi,
I’ve been using the wordpress statistics plug-in for almost two years on my original wordpress blog and my own hosted site. When I set up the independent site I needed to input my api key to get the stats going. I believe I had to do it one other time in the two years. Now, the stats have stopped working with the message that my wordpress.com account is not authorized to view the stats of the hosted site. But I can’t find a way to authorize it again. Are there instructions somewhere?

Thanks,
Paul