Same problem. Using XP SP3 Wubi and 10.10. Tried twice. Log appended. 

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04-16 23:15 ERROR  CommonBackend: The md5 of the metalink does match
04-16 23:15 ERROR  CommonBackend: Cannot authenticate the metalink file, it might be corrupt
Traceback (most recent call last):
  File "\lib\wubi\backends\common\backend.py", line 367, in get_metalink
  File "\lib\wubi\backends\common\downloader.py", line 79, in download
  File "\lib\urlgrabber\grabber.py", line 927, in urlgrab
  File "\lib\urlgrabber\grabber.py", line 845, in _retry
  File "\lib\urlgrabber\grabber.py", line 913, in retryfunc
  File "\lib\urlgrabber\grabber.py", line 1001, in __init__
  File "\lib\urlgrabber\grabber.py", line 1072, in _do_open
  File "\lib\urlgrabber\grabber.py", line 1182, in _make_request
URLGrabError: [Errno 14] HTTP Error 404: Not Found
04-16 23:15 DEBUG  TaskList: ### Finished get_metalink
04-16 23:15 DEBUG  TaskList: New task download
04-16 23:15 DEBUG  TaskList: ### Running download...
04-16 23:15 DEBUG  btdownloader: downloading http://cdimage.ubuntu.com/lucid/daily-live/20110211.1/lucid-desktop-amd64.iso.torrent > C:\ubuntu\install\lucid-desktop-amd64.iso
04-16 23:15 ERROR  TaskList: problem getting response info - HTTP Error 404: Not Found
Traceback (most recent call last):
  File "\lib\wubi\backends\common\tasklist.py", line 197, in __call__
  File "\lib\wubi\backends\common\btdownloader.py", line 79, in download
  File "\lib\bittorrent\download.py", line 129, in download
  File "\lib\wubi\backends\common\btdownloader.py", line 70, in error_callback
DownloadError: problem getting response info - HTTP Error 404: Not Found
04-16 23:15 ERROR  TaskList: Non fatal error problem getting response info - HTTP Error 404: Not Found in task download
04-16 23:15 DEBUG  TaskList: ### Finished download
04-16 23:15 DEBUG  TaskList: New task download
04-16 23:15 DEBUG  TaskList: ### Running download...
04-16 23:15 DEBUG  downloader: downloading http://cdimage.ubuntu.com/lucid/daily-live/20110211.1/lucid-desktop-amd64.iso > C:\ubuntu\install\lucid-desktop-amd64.iso
04-16 23:15 DEBUG  downloader: Download start filename=C:\ubuntu\install\lucid-desktop-amd64.iso, url=http://cdimage.ubuntu.com/lucid/daily-live/20110211.1/lucid-desktop-amd64.iso, basename=lucid-desktop-amd64.iso, length=721129472, text=None
04-16 23:31 DEBUG  TaskList: ### Finished download
04-16 23:31 DEBUG  downloader: download finished (read 721129472 bytes)
04-16 23:31 DEBUG  TaskList: New task check_iso
04-16 23:31 DEBUG  TaskList: ### Running check_iso...
04-16 23:31 DEBUG  CommonBackend: Checking C:\ubuntu\install\lucid-desktop-amd64.iso
04-16 23:31 DEBUG  Distro:   checking Ubuntu ISO C:\ubuntu\install\lucid-desktop-amd64.iso
04-16 23:31 DEBUG  WindowsBackend:   extracting .disk\info from C:\ubuntu\install\lucid-desktop-amd64.iso
04-16 23:31 DEBUG  Distro:   parsing info from str=Ubuntu 10.04.2 LTS "Lucid Lynx" - Release amd64 (20110211.1)
04-16 23:31 DEBUG  Distro:   parsed info={'name': 'Ubuntu', 'subversion': 'Release', 'version': '10.04.2', 'build': '20110211.1', 'codename': 'Lucid Lynx', 'arch': 'amd64'}
04-16 23:31 DEBUG  Distro: wrong version: 10.04.2 != 10.04.1
04-16 23:31 DEBUG  TaskList: ### Finished check_iso
04-16 23:31 ERROR  TaskList: Could not retrieve the required installation files
Traceback (most recent call last):
  File "\lib\wubi\backends\common\tasklist.py", line 197, in __call__
  File "\lib\wubi\backends\common\backend.py", line 498, in get_iso
Exception: Could not retrieve the required installation files
04-16 23:31 DEBUG  TaskList: # Cancelling tasklist
04-16 23:31 DEBUG  TaskList: # Finished tasklist
04-16 23:31 ERROR  root: Could not retrieve the required installation files
Traceback (most recent call last):
  File "\lib\wubi\application.py", line 56, in run
  File "\lib\wubi\application.py", line 130, in select_task
  File "\lib\wubi\application.py", line 156, in run_installer
  File "\lib\wubi\backends\common\tasklist.py", line 197, in __call__
  File "\lib\wubi\backends\common\backend.py", line 498, in get_iso
Exception: Could not retrieve the required installation files