Had this problem today and this is the first time I'm using ADE, so I'm a complete newbee.
After fussing around with timezones (per the online help suggested solution) and even contemplating trying every single timezone availalble, I re-downloaded the item (my item is a borrowed eBook) and the download started. (Now I need to resolve an E_STREAM_ERROR)
Try downloading the item again - hope you have more luck than I'm having.
E_STREAM_ERROR is a error with the download server of the eBook. Try a other internet browser and if not work should contact the reseller of the eBook to check the server.