Yesterday and today I had problems downloading new apps from the Windows App Store on my Windows 8 tablet.  I finally found a post in the Windows Forums about resetting the App Store Cache.  Basically, run this utility from the command line or Start | Run menu. 

wsreset.exe

Here’s the original article.  I had to use Method 3.  http://answers.microsoft.com/en-us/windows/forum/windows8_1-windows_store/windows-store-error-0x80240436/8c7dca5a-8428-4170-987b-97f47dc35d39