Comment 1 for bug 989991

The same happened to me. Base system: Win7 (64bit) Home Edition. Second system: Ubuntu 12.04 (x86) from DVD image. Use wubi.exe from web site http://releases.ubuntu.com/12.04/wubi.exe.

Tail of the wubi-12.04-rev266.log file looks like this:
...
04-29 19:57 DEBUG CommonBackend: metalink md5sums:
1e2a0b0f07bc43ab5924767a9cc03e82 ubuntu-12.04-alternate-amd64.metalink
4413660abc989dbbfe6e4abedc9a3ec1 ubuntu-12.04-alternate-i386.metalink
c29be6d58c1581d9cd679aca25db77d1 ubuntu-12.04-desktop-amd64.metalink
c7a6b99206703cfe37f1da5af1d28e3a ubuntu-12.04-desktop-i386.metalink
4e44ca9bc7ee8ab54ff9565a5437bdc2 ubuntu-12.04-server-amd64.metalink
c9cfc1dd8c65099d929189eedc157f3c ubuntu-12.04-server-i386.metalink

04-29 19:57 DEBUG TaskList: #### Finished get_metalink
04-29 19:57 DEBUG TaskList: New task get_file_md5
04-29 19:57 DEBUG TaskList: #### Running get_file_md5...
04-29 20:05 DEBUG TaskList: #### Finished get_file_md5
04-29 20:05 ERROR CommonBackend: Invalid md5 for ISO C:\ubuntu\install\installation.iso (d791352694374f1c478779f7f4447a3f != f0115a9414f578ad991dd87a99aa5c86)
None
04-29 20:05 DEBUG TaskList: ### Finished check_iso
04-29 20:05 ERROR TaskList: 'NoneType' object has no attribute 'get_info'
Traceback (most recent call last):
  File "\lib\wubi\backends\common\tasklist.py", line 197, in __call__
  File "\lib\wubi\backends\common\backend.py", line 595, in get_iso
  File "\lib\wubi\backends\common\backend.py", line 564, in use_cd
AttributeError: 'NoneType' object has no attribute 'get_info'
04-29 20:05 DEBUG TaskList: # Cancelling tasklist
04-29 20:05 DEBUG TaskList: # Finished tasklist
04-29 20:05 ERROR root: 'NoneType' object has no attribute 'get_info'
Traceback (most recent call last):
  File "\lib\wubi\application.py", line 58, in run
  File "\lib\wubi\application.py", line 132, in select_task
  File "\lib\wubi\application.py", line 158, in run_installer
  File "\lib\wubi\backends\common\tasklist.py", line 197, in __call__
  File "\lib\wubi\backends\common\backend.py", line 595, in get_iso
  File "\lib\wubi\backends\common\backend.py", line 564, in use_cd
AttributeError: 'NoneType' object has no attribute 'get_info'
<END OF FILE>

I've checked the downloaded ISO image. The result is:

51c645b87c797915ce5de4e0a72ebae24ef66628 *ubuntu-12.04-dvd-i386.iso

which matches with http://releases.ubuntu.com/12.04/SHA1SUMS