ssh and php - setgid error

[dli123]

Hi,

i'm trying to execute a command on another machine via ssh. there is an authorized key on the remote machine for the user 'www' (who's running apache).
My command looks like:
exec('ssh user@host ls', $output, $return);

The ssh-command works fine from command-line as user www but when i execute it with php it writes into the apache-errorlog: "setgid 10: Not owner".

does anybody know why?

thanks

Dominik