I don't have much else to go on with, sorry. Check your settings, check exchange URL (try accessing it from the browser as well)... did you change any other setting apart from the exchange URL?
Accessing Bitstamp API through the browser gives back the jason string (as you would expect). So i assume i am not blackflagged or anything at Bitstamp.
Settings are checked to exhaustion.
Really dont know where to change anything anymore...