Ars Technica summarize a problem with an App Store server that generated faulty DRM code for several days, causing downloaded Mac and iOS apps to crash on launch and users to hit developers with angry 1-star reviews. Apple has fixed the problem, which affected at least 120 apps and tens of thousands of users who downloaded updates or new apps during the time the problem occurred. Apple also reset the version numbers of affected apps to conceal (but not remove) the angry 1-star reviews. If you downloaded any apps around 5 July 2012, it’s worth checking for updates again. follow link
Open a Finder Window with the App Switcher
If you don't have any Finder windows open and want to switch to the Finder and open a window in one fell swoop, bring up the app switcher with Command-Tab and tab over to the Finder icon. While still holding down Command, press the Option key, and then release the Command key. You're switched to the Finder, with a new default window open for you.
Apple Fixes Crash-Causing App Store DRM Error