I had the same problem.
Stats were showing that dummy graphic instead of the dynamic diagram. I tried everything. Editing xmlrpc.php, updating, deactivating and activating.. ect., nothing worked for me. I normally use Safari, but then I switched over to Firefox and I saw that it worked just fine there. So I thought it must be a browser problem eventually. I reset Safari and voila, I had my dynamic blog stats diagram back. : )
Just another chance to fix that weird bug. Reset your Safari (browser).
