ResolutionGallery requires safe_mode to be switched off.
Since Plesk 8 safe_mode can be managed for every domain through Plesk at the CP -> Domains -> domain.tld -> Setup page. Looks for safe_mode checkbox right from 'PHP support'.
In Plesk 7.5 you can switch safe_mode off by editing /etc/php.ini file:
safe_mode = Off
restart Apache then.
Or safe_mode can be disabled per domains basis using vhost.conf. For example to disable safe_mode for domain.tld add the lines like below into the domain's vhost.conf:
php_admin_flag safe_mode off
After vhost.conf creation `/usr/local/psa/admin/sbin/websrvmng -a -v` utility should be run.