More often than not I am getting the following error message when trying to update (download updates) iOS applications from within iTunes.
Most of the time this error will ‘resolve’ itself after a couple of days updating the troublesome updates without a hitch.
To fix the issue without having to wait for days you can also delete the offending .ipa file(s) from your
C:\Users\**username**\Music\iTunes\iTunes Media\Mobile Applications
After deleting the .ipa file(s) the updates should get downloaded without any further issues.