Got a strange problem, Can sync but after sync shows there is a problem and uninstalling

though I did take them off for troubleshooting sake.

So you tried removing everything else that is USB (including any hub), except standard keyboard and mouse (if used)?

If you have not already, try this... Select the iPod in the iTunes sidebar, under DEVICES, and go to the Summary tab to the right. There is a checkbox there for Enable disk use. If you are using automatic syncing, it should be disabled (not checked) by default. Try enabling disk use and Apply the change, to see if that makes any difference.

When disk use is enabled, Windows sees the iPod's storage (as a "disk") all the time. When it is disabled, iTunes mounts the iPod's storage when it needs to do something like syncing, then unmounts the iPod's storage. I'm thinking the problem happens due to the mounting and unmounting. If it is always mounted (and seen by Windows) when connected, maybe the problem will not occur.

NOTE: With disk use enabled, you need to always eject the iPod in iTunes before physically disconnecting it from computer.

So if Enable disk use is checked, there is no error? That's probably a very important clue.

Can you live with "disk use" being enabled, at least until you can figure out the actual cause? The only real difference in iPod functionality is that you have to remember to click the eject button next to the iPod in iTunes, before disconnecting iPod from computer. People who manually manage music (instead of using automatic syncing) need to have disk use enabled all the time; they have no choice...

As for the "clue," it seems Windows does not like it when iTunes unmounts the iPod's disk, after completing the sync. The question is, WHY?

With disk use enabled, when you click the eject button in iTunes to "manually" unmount the iPod's disk, does this error come up? It's still iTunes unmounting the iPod's disk. If error does NOT happen, that's another clue.

I don't think it is caused by a hardware problem on the iPod, and any software problem on the iPod would be fixed with a Restore (which you said you did already). But can't rule out some odd hardware issue.

Try the "test" this way... Connect the iPod with iTunes running (disk mode enabled). In Windows, it should appear as a removable storage device. Eject the iPod's disk using Windows. I don't know exactly how you do it in Windows 7, but it would be the same thing you do to eject a USB flash drive or external drive, before disconnecting it.

So, with iTunes running, if you use Windows to eject the iPod (instead of iTunes), does that error come up?

ever time I connect the iPod get a pop up in the sys tray showing it's installing mass storage

That "pop up in the sys tray" does not happen every time you connect another type of "mass storage" device, like a USB external drive or flash drive, correct? It only happens with this iPod?

So, it doesn't really need to be iTunes that commands unmounting the iPod's disk; the error comes up even when Windows does the unmounting.

And, just to be complete in the test, try it again; this time, before using Windows to unmount the iPod's disk, quit iTunes so that it is no longer running in the background. Then, use Windows to unmount the iPod's disk.

When I connected it today it actually connected with out the installing mass storage message

Also, try connecting the iPod when you know iTunes is NOT running. See if iTunes running (or not) makes a difference in whether the "mass storage" message appears (or not).

I think it's not nothing, it's something, but at least you have a workaround (which is to ignore the error messages).

When I did a Google search on "ipod code 21 mass storage device," a lot of relevant links came up, so some others have the same issue. Didn't see any obvious solution...

I think it is a conflict between iTunes and some other background process Windows is running. I believe there is a background process called iTunes Helper (separate from the iTunes app), that runs all the time in the background and does things like recognize when an iPod is connected, to launch iTunes automatically. So even when iTunes (the app) is not running, iTunes Helper is still running. Maybe it is related to the problem. It may even be some security software you have running that interferes with iTunes.

If you have an Apple Store nearby, you can make a reservation at the Genius Bar. They can check to make sure it's not a hardware problem, and maybe they will know the exact cause.

Here's one more thing you can try... I tried it a few weeks ago on my 5th gen nano, just to make sure doing it would not cause any problems (before I suggested to others to try it). I don't have a 6th gen nano, but I can't see how it would be any different.

Connect the nano so that it appears as a disk to Windows when iTunes is NOT running. Use Windows to reformat the nano's storage, like it was a USB flash drive. Don't use the "quick" format option; do a FULL format. Use the "FAT" format type (although it probably does not matter).

When formatting completes, run iTunes. iTunes should recognize the iPod and tell you that it needs to be restored. Run a Restore.

I see that you already tried doing a Restore, but I'm not sure how Restore works, exactly. It may just erase the iPod's storage without doing a reformat. If it was previously used on a Mac, then Restore would need to do a complete reformat to change the format type from Mac to Windows. But in your case, it was already formatted for Windows. So now, you used Windows to definitely reformat it. See if doing a Restore this time makes any difference.