I have had quite a few applications on my iPhone for a while now and they worked all right. Now my sis got a new iPhone and she wanted those Apps so I tried syncing them and I got 80% of them on and others are showing an error. For some reason beyond me. The error it shows is: And for troubleshoot it redirects me to this page: http://support.apple.com/kb/TS1702 I followed all the steps except for "De-authorize and Authorize" your iTunes account as I don't know how to do that. Also to check whether everything works well on my iPhone I synced it and I had a couple of new Apps on my account which were not yet on my iPhone and they were not getting installed on my iPhone by showing the exact same error message. Someone please suggest some solution, Thanks.