I think the problem might be with your firewall, corrupted diablo 3 files, or with the battlenet cache folders. Disabling firewall, using repair on launcher, deleting cache folders, or reinstalling diablo 3 might fix it. Try the list below to narrow down your problem, so others can help you if you cannot fix your problem.
The list below will fix most installing, patching update, game loading, login, or crashing errors:
1) Disable or turn off your firewall, sometimes even if disable the firewall still works and need to be uninstalled. (Do not uninstall firewall/antivirus yet)
2) Run the repair tool on the launcher, see if it fix your problem.
3) Go into internet explorer, go tools, internet options, lan settings, check automatically detect settings and uncheck use automatic config scrip/use a proxy server. If above does not work, go advanced in tool options, reset internet explorer settings, sometimes spyware change your settings.
4) Go microsoft website and update your windows and internet explorer, found out battlenet update use internet explorer for patch download.
5) For Streaming Failure error, Go C:\Program Files\Diablo III or similar one in your windows, delete Diablo III.mfil (when you run launcher they reinstall these and make a backup copy in case)
6) Deleting Battle.net Cache folders: Go C:\Documents and Settings\All Users\Application Data or similar one in your windows, delete battlenet and blizzard entertainment folder (when you run launcher they reinstall these and make a backup copy in case) If you cannot see this Application Data folder, go C:\Documents and Settings, go tools, folder options, view, check view hidden files and folders. For Windows Vista/7: C:\ProgramData\ is the same as Application Data for windows xp.
7) Go Start menu, run, type in msconfig for windows xp or similar one in windows 7/8, go general, set selective startup, disable all items in start up. Go services, hide all microsoft services, disable all others (remember your settings here change back to it later) Restart your windows. Try install diablo 3 or patch up date with launcher again, and try repair tool in launcher.
8) If none of the above works, uninstall your firewall and antivirus. Restart computer, try install diablo 3, patch update, repair tool, and load the game.
9) Uninstall diablo 3 and reinstall diablo 3 trying everything listed above.
Source for more info with forum links:http://us.battle.net/d3/en/forum/topic/4904620655http://us.battle.net/d3/en/forum/topic/4926594436