I have a similar "update failed" problem when trying to download minecraft.jar for voltz or just voltz files in general. I run Windows 7 64bit with 4gb of ram to allocate in the options menu of the launcher and manually set the launcher for the recommended build 1.0.11, also the laucher version is 1.1.2.0. I've tried deleting the voltz folder, clearing the cache, deleting the contents of temp manually, but the result remains the same no matter what I've tried. Is there a fix for this? I've looked all over for possible fixes, but no luck.