i solved the problem
after some apache log analysis i figured out, that there is a problem with mod_ssl ...
[error] mod_ssl: Child could not open SSLMutex lockfile /var/log/httpd/ssl_mutex.1986 (System error follows)
[error] System: Permission denied (errno: 13)
in the end in chown'ed and chgrp'ed /var/log/httpd/ to "nobody" and - tada - no problem with the admin web interface
greets