PS4 New Install 500: Internal server error on checkout

I've just installed PS4, upgraded from PS3. I have modified my design and entered all of my settings. I have chosen paypal standard for my payment processor. (Im in Canada, hope that still works?)

Everything seems to be working, and looking, just fine until I try to checkout. I have my test products added to the cart, I can login but when I hit the checkout button the page seems to hang for a long time.
After a few minutes the confirm page finally come on with just this error message:
500: Internal server error
This error is generated when a script running on the server could not be implemented or permissions are incorrectly assigned for files or directories
Troubleshooting suggestions:
Temporarily disable any rewrite rules by renaming your .htaccess file if it exists.
Ensure that any CGI or Perl scripts have at least .755. permissions.
If trying to run PHP and you get this error, you may have an invalid php.ini in your /cgi-bin, or may be missing your php.dat file in this folder.