I am having the same problem. I get through about 50% and it says failed. I have tried Foxfire and Google. It won't work. I still have version 17 and not 18. I have done everything that it ask me to do. So I need help desperately.
I've branched your post out to a new discussion and updated the description to more accurately reflect the problem. In the thread that you replied to, the original poster was actually getting all the way through the installation, but was still being prompted to install Flash by the content they were trying to view. This is not the issue that you're having.
I don't know anything about what operating system you're using, but one of these should help:
If you haven't rebooted yet, that's a great place to start. At minimum, it will eliminate a bunch of potential roadblocks for other steps.
Collecting and posting the logs would help us improve the product, and the links to the offline installers at the bottom of the guide should get you going.