Until today, I had blocked 99% of all the ad networks that were listed. On the advice of an AdSense account optimizer, I am testing running all ad networks again. I had 3 ads per page; one a 728x90 ROS top page header. This top AdSense spot seems to loading very slow and I am seeing this message in Firefox "Read www.gstatic.com"

Has anyone encountered this before?

The top ad does load, but very slowly.