I'm getting "No apache MPM package installed" when trying to configure virtual hosts on apache2.2.

I compiled apache2.2 from source and I did not use --with-mpm=NAME option. I thought it will compile with default one then. So the question is, is there any way to check if MPM is installed indeed and I only need to enable it somewhere? If it is not, is there any way to add it without recompiling apache? Or, is there any way to have virtual hosts without it at all?

I was doing vhost configuration as per this example. Thanks in advance for your help ;)

EDIT: prefork is installed. The question is, why after a2ensite / a2dissite and /etc/init.d/apache2 reload I still get error "No MPM package installed"...