I am getting this message:
Unable to write file: /var/www/vhosts/examplesite.com/httpdocs/wp-content/plugins/files/civicrm/upload/version-info-cache.json
Please check your system file permissions.
But this files doesn't seem to exist in that location. Should it exst there or could there be something wrong in my settings?
(CiviCRM 4.6.8 and Wordpress 4.3.1)
Make sure that the folder /var/www/vhosts/examplesite.com/httpdocs/wp-content/plugins/files/civicrm/ is writable to the webserver user.
The simplest solution is to set the permissions on that folder to be read/write for ALL users.
A better solution is to configure the permissions so that they are open to your user account and the webserver alone, but not other users on the same hosting server. How you approach this depends on the hosting environment and probably requires learning how to manage filesystem permissions.
See also:
Check your permissions for /var/www/vhosts/examplesite.com/httpdocs/wp-content/plugins/files/civicrm/upload. It's not surprising that the file in the error doesn't exist when you check--CiviCRM hasn't had the ability to create it!
The most common issue is that the folder is owned by your SSH user, not the user that Apache runs as.
