iTunes generic app icons

Most of the icons for my iPad apps in iTunes have changed to a generic "A" inside the icon. Some of them I was able to get back by clicking on the icon, but that does not work on the many remaining in this condition. There is a screenshot below and/ or here: https://dl.dropbox.com/u/16195619/iPad%20Generic%20icons. If I connect the iPad to the computer, select it in iTunes and examine its app screens, the icons in the screens are all OK, but the scrolling list under Sync Apps to the left of the screens matches the assortment of generic and proper icons.

Two days ago I attached a new WD Elements 1T drive to my Airport router and moved my iTunes Media Folder there, copying about 100 GB of mostly music. I presume this is now where my iPad backup and apps are, as well (yes?). Everything was fine yesterday after the move, but this problem surfaced today. I am running iTunes 10.6.1 under Snow Leopard 10.6.8 on 2008 Intel MacBook5,1 with 8 GB of RAM. I back my original iPad, running iOS 5.1.1, up to this computer via cable or wifi, but I don't use iCloud.

I have restarted both computer and iPad multiple times and re-synced multiple time. One oddity was that a newly added app did not sync until I dragged it manually to the iPad. All icons on the iPad are normal and seem to be functioning normally. At that point I noticed that iTunes had reverted the location of my library to the computer, not the new disk. After Disk Utility reported no problems on the new drive (although I can't fix disk permissions on that drive; is that normal?), I changed the location back to the new drive and consolidated the library, none of which had any effect on the icons. Fixing permissions on the computer doesn't help. The only thing that works so far is to delete a generic app and to reinstall it. Before I do that 50 times, I'd like to figure out what has gone wrong, so that I don't have to do it again.

Any and all suggestions gratefully appreciated.