Q: Trying to upgrade to OS Maverick. Get message "this computer cannot be upgraded". Checked all tech specs, match requirements. Is there a way to determine what prevents instalation?

I don't know what determines what prevents installation, but these are the models that it can be installed on:

https://www.apple.com/osx/specs/ so if your Mac isn't one of them your Mac cannot be upgraded as per the message you are getting.

Check that your computer is compatible with Mountain Lion/Mavericks.

To check the model number hold down the option/alt key, go to the Apple menu and select System Information.

• iMac (Mid 2007 or newer) model number 7,1 or higher
• MacBook (Late 2008 Aluminum, or Early 2009 or newer) model number 5,1 or higher
• MacBook Pro (Mid/Late 2007 or newer) model number 3,1 or higher
• MacBook Air (Late 2008 or newer) model number 2,1 or higher
• Mac mini (Early 2009 or newer) model number 3,1 or higher
• Mac Pro (Early 2008 or newer) model number 3,1 or higher
• Xserve (Early 2009) model number 3,1 or higher

That's odd . How far do you get - are you able to do the download or do you get the message as soon as you try do start the download?

Ignore my second post - I see you got the answer (Eric expanded on the detail in the link I posted).

You are welcome.