sorry but if you do what I said above you can not be having the same problem.
forget about what version you have currently.
all you need to do is download the current version complete zip file, not the update version.
then, unzip it on your computer.
remove the blank config.php file from the phpBB3 folder.
using your ftp, copy your current config.php file to your computer for safe keeping.
now, upload all of the new phpBB3 files and folders to your server letting them overwrite the ones that are there.
now, in your browser, go to:
let it run,
then, in the ftp delete the folder named "install"
if you follow these instructions exactly and in order, it WILL work with no problems.
take our word for it and just do it.
do not do anything I didn't tell you and be sure to do everything I told you and you will be fine.
you are making this way more difficult than it has to be.