it's not your iPad it's the App store having trouble for the last couple of days. you can update by doing this
1. go to App Store
2. press Purchased instead of Updates
3. scroll down & you will see each App that needs UPDATING - press on each one separately; update download starts
4. do this for both iPhone Apps & iPad Apps (top left corner)
this worked wll for me; hope it works well for all until Apple can fix whatever mess caused this.
this was a much older way we used to have to do it; well & also put in the password each time.
funny that this is only on the iPad & not the iPhone! tho i had a problem with a couple on the iPhone because i purchased them with a very old Apple ID & password i haven't used in years....
i'd be interested to know if any of you used the new iCloud with the beta iWorks on it. that's when all the problems started for me - & not just with the App store. iCloud set up a new account for me using that old ID & Password; lost all contacts, calendars, memos, reminders. finally found the old account & everything restored.