This computer is no longer authorised for purchased items

Solution 1:

You've probably authorised the computer with a different iTunes account from the one that the iPad is using. Have you tried deauthorising it and then authorising it again? (If you've purchased iPad apps on both the iPad and the Mac, using different iTunes accounts, then you've got a problem.)

Solution 2:

I had this same problem. I discovered that at some time in the past I had created another AppleID. My iPhone was "logged" in using one ID, I was trying to sync iTunes using a different ID. Go to Settings> iTunes & App Store and note what your AppleID is. Now in iTunes check to see if you are logged in (upper right near the search box) under a different ID. If you are, log out and try store>authorize using the same ID as your iPhone. I had to de-authorize the computer first because it was registered somehow under the other ID. Then re-authorize using the same ID as my phone. It worked for me.