Osx update error

Sounds like some sort of silently corrupted download (I had an old router that did this occasionally). Try a different connection using completely different modems, routers and access points. Maybe even a different internet provider at a friend's house or office.

This is an ancient question (bumped by Community♦), but invalid checksum doesn't have anything to do with admin privileges, it is a bad download.

Since you tried multiple times you are either not getting the file despite the multiple tries, or the original file you are downloading is not complete.

I would look for another way to get the update.