PPRuNe Pop
Are you using a Proxy Service ? - Which Browser (maybe not as you say not one instance, IE 8 and later) -
Anti Malware Software causing Probs ? - A temp problem with your ISP.
I assume its a Windows based System - Perhaps an add-in that blocks Third party content in the browser (legitimate) is causing problems
Or !!!!! on the black side - your "Man in the Middle" has given himself away because the battery backup on his server has finally given up.
No doubt Mix or MB will help.