I just had this problem, trying to update Pages on my iPad 1. Found the lost app on another iTunes account that I set up years ago and forgot I had. Apparently I managed to download the original Pages on my old account. So to update, I had to sign out of iTunes from my "new" account, then sign back in to "old" account. Thank goodness I kept the old password. Once in under the old ID, I just went to apps, tapped the lower right corner to find update able apps,went there, and there was Pages, waiting to be up dated. All this was done with my iPad disconnected from iMac. Once the upload was complete, connected iPad to iMac with iTunes on the screen (still old iTunes acct.). iPad came up under devices, in left iTunes column. The iPad sync/update screen appeared & I checked to be sure Pages checked to be synced in apps section. Then touched "sync". It took about 15 minutes to update Pages. When completed, clicked left column to disconnect iPad, then unplugged it. Signed out of old iTunes ID, closed out iTunes, restarted the computer, and that was that. Months ago couldn't figure out why some of my iTunes items were missing, so I emailed their customer service. They quickly emailed me back reminding me I had 2 iTunes accounts, and gave me the username (email addy). Now I am careful to check what account is open when I buy music & apps. I was told there is no way they can combine accounts & funds, so I guess I'm just going to give them my last 97 cents in the old account. Hope this helps.