W
There's not much documentation for this error in regards to Windows Phones, so we'll have to try some general things first.
Clearing the cache and doing a soft reset fixes a large number of issues, so lets do that first. Go to Settings -> Applications -> Internet Explorer and tap on Delete History. When that finishes, hold Power and Volume Down for 15 seconds until the phone restarts. After it's back on, go to Settings -> Email+Accounts. Tap and hold on your Microsoft Account and select Sync. Then see if you can download or update any apps.
If that doesn't fix it, go to Settings -> Date+Time, and turn off automatic updates and see if that works.
The error itself implies something is missing with the app files, but the fact that this isn't effecting everyone leads me to believe otherwise for now.
Let us know how it goes!
Regards,
Kevin J S