I reinstalled, as you said, and it looks like the installer has fixed the problem.
Thanks a lot, as always.
If I can abuse you a little bit more, this reinstall procedure could be used as a kind of "cure all" settings?
I mean, I tried a few other steps before reinstalling, but the server owner was quite upset about this problem, and I decided to reinstall. Also, the server was quite new, having only 4 websites to be reconfigured in case something went wrong. In short, a very small risk of losing everything.
What if other sysadmin had these problems, is it advisable to do a reinstall, even on a server with hundreds of websites?