I had nothing but drama's downloading the file onto SD , I'd get 99% into in and then it would stop (different problem to yours I think) but I tried heaps of times .
I wondered if it was my firewal protection on my computer but in the end One of the fellas on here lent me his card and it updated fine (thanks again dave ).
I'd try doing the download from another computer running different antivirus maybe?
I'm definately no expert , just breath deep and resist the urge to smash your sounder & computer.