Problems with PHP support

[Energymedia]

Hi there.
I've got a strange problem and, after a night of searching on the server without success I've decided to ask for a help.
I'm using IspCp 1.04 on Debian 5, for some domains I'm hosting in my server.
Yesterday I've tried to add a domain and also an alias domain. Both of them have remained unsuccessfully created (red sign, not green status). OK. I've thought that if I'll delete and re-create it will be OK. But delete process failed without explanations in IspCp. The domain directory have been deleted but configuration files were still there. I've stopped the daemon, apache, bind, and tried to clean by hand, for a future re-creation of the account.
Everything went aparently OK, apache started OK, I have re-created the domain, with all necessary settings, PHP and CGI support. The domain is now green status, the config files look OK aparently, the default site of that domain works (html-only), but any kind of PHP script I try to use in this account, it gives me a 500 "Internal server error". I've thought that the user/group in the sequence added to ispcp.conf is different from the real user/group, but the problem seems to be in another place. Any suggestion is appreciated.

Note. The old accounts are not affected by this problem, I have created also a subdomain in my old domain and it works fine. Only this new added domain has this FCGI problem.