I haven't needed to run the kindlefix script so I can't give specific instructions but from searching the forum (using the search term "kindlefix"), you might want to double check the following (with links to the posts):
There are no letters "O" in the Kindle PID, it will always be a "0" (zero).
Make sure you've deleted previous books before re-downloading them.
Make sure there are no spaces in the PID and all letters are capitalized.
Also make sure to keep the "*" in the PID.
The kindlefix.py, prc.py scripts and book are in the same folder.
The book title should have quotes around it.
kindlefix.py "BookTitle.prc" KindlePID
That's it from me. The experienced users should be waking up soon to give you more help.