Hi, I am running ElCap and I need to install Mavericks in a separate partition in order to run apps which are incompatible with ElCap. However, each time I start up Mac OS X 10.9 Installer I get a message that says "This copy of Install OS application is too old to be opened on this version of OS X” and I have no choice but to quit. Or, once I managed to load the Mavericks installer thumb drive which I had created back then but strangely enough the installer would only install ElCap, not Mavericks. I don't know how this happened but is there a way to install an older version of Mac OS X on a hard disk? BTW I'm not downgrading the existing ElCap. I just want to install a fresh copy of Mavericks in a separate partition so that I can switch between both versions of OS X.