iTunes cancels manual drag and drop sync
I have a 4th Gen iPod Touch which will not sync with iTunes music that I manually drag and drop into the iPod.
When I drag music into the iPod, iTunes will sometimes update the iPod with the music, whilst at other times it tells me that the sync process is "cancelled", leaving greyed out music files in the iPod which will not update. Once this has happened, the storage space at the bottom of the screen shows there are no music files, just "other" file types. It is not possible to play any of the files whether the iPod is connected to iTunes or not, I just get a circle symbol with an exclamation mark in it.
I have the iPod set to manually manage music and convert the files to 128kbps (it's only 8GB capacity).
I have restored the iPod multiple times over the last two days and I still get the problem. Does anyone have any ideas how to get my music onto this iPod?
iPod touch, OS X Mavericks (10.9.5)