I have been seeing this a lot, I think the Apps have been updated prior to Friday's official release. I had to remove the app, then go the the Store (from the Metro Win8 page) and re-install it. Every app is still free from what I have seen, so it is just a hassle at this point. Oh man, your store app is acting up? That could be a Catch 22, as you might imagine.
To remove an acting-up app (these directions are not for a touch screen! just for keyboard/mouse systems)
1. Tap windows button on keyboard (takes you to the Start screen [aka Metro screen]) if you are on the Desktop side.
2. Right click on the offending app and left click on uninstall.
3. Go to the Store app (green) and hunt the replacement app and reinstall it.
If you cannot fix the store app you may need to refresh Windows 8, as detailed in the following URL.
URL deleted.... I cannot vouch for the system changes that Refeshing will enact...