iPod Touch won't sync after restoring Library

My iTunes library is stored on an external harddrive and, when I accidentally unplugged it once, it got totally messed up, because iTunes set up a new and empty library somewhere else. I plugged the harddrive back in and moved everything back into the library.
Afterwards it said that it could not sync my iPod Touch, because it was synced to a different library and could only be synced with one at a time. As I thought that I had everything in the "new" library, so that I could easily resync it onto the iPod, I said that it was fine to sync it. Exept that it didn't. I selected everything that I already had on there (ready to wait for hours until it was done putting them back on), which clearly left 6GB on the iPod empty, but it said that it could not sync because it would require 9 additional GB.

Does anyone know what's wrong and what I could do to fix it?