Here's the log entry: Premature end of script headers: [...]/mwiki/config/index.php
Obviously it's not being run properly indeed. I already contacted my ISP but any additional hint is welcome.
Hm, nothing more? That's a shame. Is there a PHP equivalent of perl's "-w", does anyone know? Or, for that matter, a really easy way of getting it to print messages to stderr (like "Got here." etc) so that you can see if they appear in the Apache log (as I understand it, anything sent to stderr will)?
If it's not even *beginning* to run, I don't know how you could work out what's wrong, to be honest - all that error tells you is that Apache never got hold of the output, which could mean anything, couldn't it?