I got a very strange usergroup setting by ISPConfig: SuexecUserGroup nobody web15 How could that be happend? What I did is: creating an new user and a new domain. Later on I gave that new user permissions to use php as php-fcgi. That I got en internal server error and I only found that strange nobody user. This must be the fault. I've even deleted the website and user and created both new but with the same result: nobody How ISPC chance that?
I guess your website has no administartor user yet? Create a dmin user and the suexec user will be changed from your apache user (nobody) to the admin user of the website.