My favorite answer in cases like this - an error immediately upon installing the software - is to get a fresh copy of the zip package, unzip it on your computer, delete all the files in the "inc" folder from your server, then upload the fresh copy of "inc" that you just unzipped.

The theory is that somewhere a file got corrupted. Could have been anywhere in the process of getting it to your server, so if you start with a brand new copy of the package and simply replace huge chunks you've got a good chance of replacing the one file that actually needs replacing.

If it doesn't help at least we'll know it's probably not any of the files in that folder!

You're missing the "xml" extension in your PHP.
It is enabled by default in PHP and it seems like your host has disabled it. Refer them to http://php.net/manual/ref.xml.php.