Thanks Naseem, this fixed it for me.
In my configuration.php I had:
public $log_path = '/home/mysitene/public_html/logs/';
public $tmp_path = '/home/mysitene/public_html/tmp';
i.e. a contraction of "mysite.net.au" - mysitene
However it *should* have been this:
public $log_path = '/home/mysitenet/public_html/logs/';
public $tmp_path = '/home/mysitenet/public_html/tmp';
That is, with a 't'.
After I changed those two paths, I was able to upload to RokGallery without error.
(Note: I also installed latest version of RG and Joomla)