I had an error while installing (but in the end, the installer told me it was OK). I've seen some errors that I never found before while upgrading, so I tried to login to the control panel and it didn't work. Normal webserver (port 80) didn't work neither.
So I tried to run ./setup again, looking through messages: it stopped while compiling clamAV (then, it didn't ask me the administrator's mail for SpamAssassin), and tried to run some other files, but the whole install_ispconfig was deleted.
After some research on the install files, I found that I could avoid the clamAV installation by editing install_ispconfig/compile_aps/compile and removing some lines there; then it worked OK.
It happened to me in a Fedora 7 install working right, and with previous upgrades with no problems. I've also upgraded some hours before 3 different Fedora version's servers with no problems.
I don't know it that could cause you the problems. Here's it's midnight now so I'll go to sleep -server's just working now- and tomorrow I'll see if I can tell which was the exact reason or if I could do something to clamAV before (but I never use antivirus on mailboxes in that server and I never touched its config or files; and the server hasn't been restarted 'till two or three previous upgrades.....!
Hope that helps a bit for if someone has the same problem. If it isn't related, just delete it !!!
PS: I've seen the error I got during installation on other boards. Here's the message:
others.h: In function 'cli_getpagesize':
others.h:363: error: '_SC_PAGESIZE' undeclared (first use in this
others.h:363: error: (Each undeclared identifier is reported only once
others.h:363: error: for each function it appears in.)