Bad news I am afraid.
I redownloaded the zip file you mentioned, and tried a complete install from scratch.
First of all the Connections folder again would not write, so I manually inserted the relevant data, copying it from a previous install (and adjusting the database name).
Then as the installation proceeded, I got a 500 error on the page:
I had a look into the file to see if there was anything outstandingly obvious I could fix so the install would continue, and decided it best not to follow that route, on this occasion.
ftp credentials in the private area if you require them to adjust any files