Ok, I'm not a true SysAdmin then I can not help you to read and setup your php.it but...I can help you in order to find what happens with the plugin.
I think that your server has an older php compiler. Are you using Apache? If yes which version?
Because all issues that you've identified are caused by a bad interpret about php code. Now I try explain to you why.
"quick-guide.php" is a file that will contain some instructions which help users to configure the plugin.
It will not be useful until next 5.1.1 version of plugin, when "quick-guide.php" will come with some updates.
Maybe the error can be generated by line 14 about "quick-guide.php".
So, try to substitute the tag "<?" with "<?php", save the file and try again to reactivate the plugin.
The error "unexpected $end" should disappear, else try to delete all "quick-guide.php" file content and save it again.
Obviously you must mantain the previous changes made to your "referral-mode.php" file. (deleting line 552).
After this send me news about.
No one has encountered the same errors, and there are more than 250 websites with this plugin activated and working! Please check your Php compiler version!