Can't open dmg for combo update to 10.14: corrupt image I've downloaded macOSUpdCombo10.14.6.dmg from the official apple site twice now in order to update my 10.10 to 10.14, both times when I try to open the dmg I am told that it can't be opened as the image is corrupt.

I'm at a loss, this isn't happening with other dmg files I have, I've run the disk utility function verify on my drive and it reports no errors. 
 Is it the file? Am I doing something wrong?  Any insights would be appreciated.
Get macOS Mojave directly from the App Store and install it. This will give you the most recent version of 10.14.6, you won't need to run the combo updater afterwards.