Okay so here is the story..
I had just bought this Mac... I tried installing some software, and nothing was installing... kept getting this stupid error.
The Installer encountered an error that caused the installation to fail. Contact the software manufacturer for assistance.
So I thought it was like that for one particular program, so I began looking on the internet. Eventually I just forgot about it, until I tried to install another piece of software. Again the same issue... I soon realized after that it was happening to every single piece of software that I was trying to install that involved an installer package...
So then I tried to download and install El Capitan from scratch... But now I have run into another issue... app store won't download it... I'm stuck with this spinning wheel at the top left corner where the "Back" and "Forward" buttons are with the "Download" button grayed out after clicking on it. No response or any indication that it is downloading.
Any ideas? Support is out for the day, so I hope I can get an answer by tonight.