Ubuntu wubi installation is now at 10.04 “Lucid Lynx” and it is not recommended to upgrade to 10.10 “Maverick Meerkat”. I tried doing this yesterday on my test PC and now I am not able to reboot into Ubuntu.
Fix is currently being worked upon: https://bugs.launchpad.net/wubi/+bug/653134
There are many posts that describe how to workaround this problem:
I uninstalled wubi and will try a full installation 64-bit from Live CD. Seems like wubi is just for testing/ simulation of Ubuntu on Windows.