I see this error on my master site GUI. There is a snapin Master Control where you see all you site status and you can disabled/enable lot of configurations like notification,service checks etc. I tested this behaviour on my master site 1.5.0p24 and 1.6.0p11 and 1.6.0p12 and the issue remains the same.
So, initially when I login to my master site, it takes more than 5 minutes to load the complete webpage and then I check the Master control snapin and I see this error once the page is loaded.