I was successfully creating Windows Store Apps using Visual Studio 2013, using my dev account. VS has recently re-registered my ID as well.
Today, any Strore App (including "Mail", "Store", "PC Settings"...) not running nor any of project is not launching when I start debugging. It gives dialog as shown below. Also, as the app starts showing as installed in the start screen, when I tap it there, it doesn't run. Just splash screen flashes for a few seconds and then disappears.
---------------------------
Microsoft Visual Studio
---------------------------
Unable to activate Windows Store app '3a829624-c06f-426b-8186-9312684573a2_bs4v6h88qrjp4!App'. The activation request failed with error 'This app does not support the contract specified or is not installed'.
See help for advice on troubleshooting the issue.
---------------------------
OK Help
---------------------------
If a post solves the problem you asked, please mark it as Answer.