Wirelessly posted (Mozilla/5.0 (iPhone; U; CPU iPhone OS 4_2 like Mac OS X; en) AppleWebKit/533.17.9 (KHTML, like Gecko) Version/5.0.2 Mobile/8C134 Safari/6533.18.5)
My iPhone 4 started doing this after I updated activator recently, but its on 4.1 jailbroken with greenpoison. Did you update anything in cydia recently? Check that, it worked for me.