ANOTHER SOLUTION - for people who dont want to Sync Music and would rather "Manually manage music and videos" and have got this option ticked under the iPod's summary:
(read the italics at the bottom of this post if you can't be bothered reading my trial and error experimentation talk)
I followed pretty much every easy solution proposed on this thread and nothing worked for me in terms of getting particular MANUALLY CHOSEN songs to sync. I have enough confidence in my software knowledge instincts to make a guess that I could figure this out without uninstalling/reinstalling, backing up/restoring anything at all. And I did 🙂
I didn't want to have to manually go through my library either and bring the songs back over, it took me nine hours to pick what songs I wanted the first time and I really didn't want to have to do that again =/
That nine hour session, I hadn't realised only some of my songs were transfering properly to my iPod and others were not. They were grey (not black) and had a round sync icon next to them. To me it looked like they were "pending" synchronisation. So from that idea I thought, well if it's on this kind of "waiting list", maybe iTunes forgot about the list, so I need to remind it?
I saw a post above about taking "drastic measure that really don't do anything" so I started off with removing a massive app (Google Earth) off my iPod then resyncing it back onto it from my library but pulling the cable out in the middle of the process then reseting my iPod (home + sleep/wake buttons together).
I then experimented with the autofill function and clicked that and saw my whole entire library on the "waiting list" in grey under my iPod's music. I was getting close! But I DON'T want my whole library, just that initial hand-picked list...
So I pulled the cable out while it was syncing, reset my iPod again for extra luck, picked ONE song that I had never picked to transfer to my iPod before (was neither fully transfered [in black] or on the iPod Music "waiting list" [in grey]) and dragged it to my iPod...
It took a minute of waiting and staring at my iTunes screen waiting for the status to change from "Getting ready to update files..." to "Transfering 1 of 1339: ...." YUSSSS I HAVE REACHED SUCCESS!
I had finally managed to "wake up" iTunes to the fact there are a thousand songs waiting to be transfered over 🙂
I did a lot of mucking around and things that probably won't be necessary to achieve the same result but what I think SHOULD work without all of that messing about:
-In iTunes: Edit > Preferences > Devices > tick "Prevent iPods, iPads from syncing automatically
-In iTunes: left sidebar go to your iPod > Summary > uncheck "Sync with this iPod over wifi"
-reset your device (home + sleep/wake buttons together) and your computer.
-Wait for everything to load up. Open iTunes, connect iPod via cable, drag a song into your iPod that is not already on it or "greyed out"
-See if iTunes recognises the list of songs in grey waiting to be transfered and does it!
If it works, feel free to change back any settings like automatic sync and wifi sync 🙂
Swwwweeeeeeeeeeeeeeeeeeeeet, let me know what you do and if it works or not 🙂
I'm so happyy I got all my music 😀