Wiki plugin breaks my site: all pages are blank

Dear WpmuDev Team,
My site is and works fine, but when I install wiki plugin it works fine for 5 minutes and after 5-10 minutes it breaks my site: all pages are blank.
I have a dedicated server with 16 GB of Ram, Intel Core i5-2400 4x3.1+ GHz and php memory limit is 1024 MB.
In the error log of my server there is only this error: "PHP Warning: is_writable(): open_basedir restriction in effect. File(/) is not within the allowed path(s): (/var/www/vhosts/ in /var/www/vhosts/ on line 133", but I don't know if it is the cause of my issue with wiki plugin.
Any help?
Thanks in advance