I had problems with error -48, unable to update and eject, files in use etc. Nothing would work, even spent 3 hours on phone to Apple tech support, they couldn't fix it either. In desperation I performed an Archive and Install which at time of writing has worked, Nano 8gb now working perfectly for the first time since purchase. Info @
http://docs.info.apple.com/article.html?artnum=107120
Procedure was easy and all network settings etc can be retained, even my iTunes library remained intact. Remains to be seen whether this is a permanent fix, but so far so good.