If all else fails, drag & drop the dmg file onto the Disky copy program icon. Be that within the dock or within the utilities' app's folder.

The steps are:
1. Downld using Safari.

2. If safari doesn't use disk copy as the defalt program to open dmg files then your stuffit preferences need to be changed!!!! Otherwise this issue will forever cause you headaches!!!
(Do NOT allow stuffit to be your default to open dmg files. Disk copy is designed specifically for this purpose!)

3. After downlding, then drag & drop the dmg file onto disk copy which is the safest way to do it!