I have the same problem. I have a Dell D630, nVidia 135, 1440*900 machine with OSX Yosemite 10.10.3 which was installed with myhack 3.x and than i did make my Extra with edp6.app for at least 10 or 11 month.
Now I try to install epd7.app. When i double click on edp7.app the installer does start, it does connect to your website, it does download some files, but it does than tell, that it can not continue to install edp7.app, because "there is chameleon and clover installed" at my hard disk.
There is defenitely no clover installed at my hard disk, because the efi partition is empty (and I never did install clover on my installation).
So there is a major bug in the installer of edp7.app, that does prevent to install edp7. I ask:
Maybe: must I uninstall edp6 first?
If yes, how can i uninstall EDP6.app?
Regards
Thomas