Access denied due to security settings. Either change the permissions on the Program Files folder or put the RTDStore app in a different folder.
For the author: downloading into the app's working directory is, and always has been, a terrible idea. That's why Application Data and Downloads and Temp folders exist...
Win8/Windows RT projects:
List of desktop apps for hacked RT devices
Native Access WebServer and Libraries
WP8 Interop Unlocks
XapHandler, Root Webserver, OEM Marketplace XAPs, Bookmarklets collection (Find On Page), Interop-unlock hacks.