My classic no longer accept music from iTunes. Once connected to my MacBookPro15, iTunes says that the iPod is no longer readable. Restoration was unsuccessful. Online forums discussed the error being a result of the OS. I have no intention of upgrading to El Capitan since reports have been negative, so I continued to search the forums. The next suggested that the logic board may have gone bad, so I ordered and replaced this.
The repair guide is excellent and very true. This is a beast to open. I managed it with a little frustration and thankfully no damage. Take your time and be aware of ALL the locking clips. Once open the ribbon removal and shifting of other parts is fairly simple. Reassembly is also fairly simple.
Unfortunately this did not solve my problem. Further research indicated that reformatting the hard drive may work. I did a seven pass writeover of the drive. The iPod is no longer rejected by iTunes; however, the iPod does not retain the music once added. My next attempt will be to replace the drive.
"Once more unto the breach dear friends"