Q: I cannot install purchased, downloaded apps on my MacBook Pro.  They get to about 75% and I get an error saying "NSPortTimeoutException."  Help!

My MacBook Pro was purchased secondhand and has a number of apps from the previous owner, but anything new I try to add gets the same message.  It's running on OS X 10.6.8. The apps are in my purchases as ready to install, and I've tried various paths to install with no luck. I've double-checked system requirements for each app, and they all say they are compatible with 10.6 or higher.

I know virtually nothing about macbooks (recovering PC girl), so a detailed explanation of any fixes would be greatly appreciated.