Thanks for the fix karrde! It worked for me.
But, I don’t think this problem is dependent of OS, but something else. This plugin didn’t work for me either (after fix karrde mentioned it worked), and my host is running CentOS Linux and Apache. And like with RobertGX, I can only add one text and rss widget. But that’s enough for me as long as I can make my theme compatible with widgets and continue somehow (I hope they release new version sometime).