From WinCustomize Wiki
Issues with IconPackager 3.20.128 and Vista
With version 3.20.128, there is a bug which causes IconPackager to break the associations of the start menu default program links in Vista. The second line of text on the start menu entries, denoting the default program, disappears after applying a package.
When you try to view the default program settings in the control panel, you will find that the start menu link shows "Unknown application" instead of your desired default (IE, Firefox, Opera, etc)
Fix & Workaround
After contacting support, they have assured me that this bug is now fixed in their internal builds, and should at some point make it into the public build.
In the meantime a manual workaround is available:
in regedit, navigate to
an delete the follwing 2 keys:
Log out and back in again, and things should be back to normal.