Hi,
had the same problem with the session_save path.
Here is how I solved this:
Check the php information from zenphoto backend.
There should be an entry called:
Session.save_path
where you can see the see the default tmp folder.
Mine looks like:
/var/www/mywebspace/phptmp/
Now open the function_basics.php file from the zp-core folder and add a new line right after the php openening tag.
Add this there:
ini_set ( 'session.save_path', '/var/www/mywebspace/phptmp/' );
Please be aware that you are editing a zenphoto core file by adding this, so it is on your own risk and be sure to make a backup of the file before editing.
In my case it solves the problem with the session.save_path.
Cheers
Ralf