I think I have solved the problem. After activating all the plugins again(on the network page), the problem came back. I again deactivated all plugins and also checked that the plugins where deactivated on the site. I then activated them one by one on network, but let out the plugins I only use for that particulare site, and among those plugins I had the 3 color styles plugins. And now everything seems to be okay.
But thanks for your concern Ipstenu ??