Try another erase and install. I had to do it 3 times before everything worked properly. I don’t really understand why an install would work the third time and not the first two but It did. I too felt your frustration of leaving a rock solid 4.5 to pay money for an upgrade that dosnt work. All that said, my fcp5.04 system is allmost as solid as 4.5- it just still drops frames all over the place-
Good Luck- JP