iTunes converted my WMA files to AAC but now their playtime is listed as 0:00?

Prior to installing iTunes 10.6.1.7 so I could use a new iPod Touch, my library was a mix of MP3 and WMA. The MP3s imported fine after the install and I have had no issue adding them to my iPod or playing them on my computer. Unfortunately, iTunes seems to have failed at properly converting my WMAs to AACs, or I'm missing a step entirely that I am not aware of. This has left nearly half my Library unlistenable.

I received the prompt that it was going to convert them, clicked OK and the files were added to the Library, but their length is now listed as 0:00 and when I hit play, they skip in an instant without any sound. It says I've listened to the any of the former WMA tracks when I try to play them, because it's counting each 0:00, but the fact of the matter is, I haven't been able to listen to ANY song that was WMA. Entire albums are completely skipped.

EDIT: The time is listed as "Not available", rather than 0:00, but that's what shows in the play bar when one of the converted AAC tracks starts.

Is there any remedy for this besides tracking down all the faulty files, removing them from the library, and ripping them to my computer in MP3 format to re-import? That sounds awfully tedious for thousands of tracks, and I may not even have the original CDs for half of them anymore.

Any help would be GREATLY appreciated, thanks.