I try to install, SS 3.0.5 but I’m getting this error/warning..:
Warning: session_start(): open(/var/lib/php/session/sess_i1m5rak76dt7bj8rflbq6kinm6, O_RDWR) failed: Permission denied (13) in /var/www/vhosts/transip.nl/httpdocs/framework/dev/install/install.php5 on line 28
I'm not a server expert so could be wrong. But at a guess looks like the User set up for your VPS doesn't have read permission to /var/lib/php/session thus the open() fail.
You could try adding something like
to the top of the index.php file in your silverstripe installation. You might be able to get away with it in the mysite/_config.php file but I'm unsure at what point SS starts the session (before or after reading the _config file).