Sqlite PHP permission issue / writing to a different folder

I have two sites running off a single box that answers on different ip addresses.

Both of these sites have different root folders /var/www/ and /var/www2.

/var/www contains the main site and a sqlite database.

/var/www2 contains a few scripts that need to access that same db.

I have tried

    $db = new PDO('sqlite:/var/www/db.sqlite');

from the second site, but, I keep getting File not found, and in the logs I get

FastCGI sent in stderr: "Primary script unknown" while reading response header from upstream,``

Both of these sites work fine when reading/writing to dbs in their own folder without the path.

Can anyone advise anything?