Cannot synch music from Itunes to Ipod; odd authorization issue

That may indicate that some of your songs are old purchases from iTunes Store (from before early 2009) that have DRM (copy protection), AND a different Apple ID was used to purchase those songs. If this is the case, you probably used your current Apple ID (and password) in the Authorize This Computer dialog. And iTunes told you your Mac was already authorized for that Apple ID. You need to enter the other Apple ID (and password) for the Authorize This Computer command.

So, this problem may not be with the songs you just purchased, since current iTunes Store song purchases do not use any DRM (so authorization would not come up), and even for content with DRM (like movies, TV shows, audiobooks, and music videos), your computer is authorized for your current Apple ID.

Does the error message give you a list of songs that have this problem?

If the error message did not provide a list of items, you can check in your iTunes music library. Show your iTunes music library using the Songs view (selected from control at right end of horizontal bar) to show a plain list with columns. If the Kind column is not visible on the list, make it visible (right-click the heading row to show/hide columns). Click on the heading for the Kind column to sort your song list by Kind. This groups your songs on the list by Kind. See if you can find any songs with Kind of Protected AAC audio file. I "upgraded" my old DRM'd songs too (using iTunes Match), but I have a few dozen left that are DRM'd ("Protected") because iTunes no longer sold those songs.

If you have one or more songs that have Protected AAC audio file for Kind, they may be what is causing the authorization message. These would have been purchased before early 2009, and not upgraded.

i think i bought them from another site and they were supposed to be DRM free.

That's not possible. The only DRM used in iTunes is Apple's DRM scheme (called FairPlay). You would not be able to import songs with non-Apple DRM into iTunes. Songs purchased from most other places, such as Amazon MP3 Store, do not use DRM either, like current song purchases from iTunes Store.

Those files are on my ipod, and i found a way to drop and drag music from my library to the ipod (after great frustration).

I assume that's in iTunes, using the Manually manage music method (drag and drop songs on iPod in iTunes). You would still have the same problem as automatic syncing, if the songs you added manually used DRM, and your computer is not authorized for the Apple ID. Therefore, I think the problem is something else. Those songs that you loaded manually ARE authorized, because you did not get the error message. That means the authorization error you got before came from something else. For example, if you had any movies, TV shows, music videos, or audiobooks, set up to automatically sync before, that may have been the reason for the authorization error message. Those other media types used DRM in the past, and still use DRM today. If you want to set it up to sync automatically again, I would set it up making sure only Sync Music is checked on the screens for setting up iPod's automatic syncing.

If it says Purchased AAC audio file, those songs do not use DRM. They are purchases from after early 2009, when Apple was allowed by content producers to stop using DRM for songs sold by iTunes Store. They are not the cause of authorization error message when syncing songs to iPod.

Restore would be a sensible thing to try next.

So, if most of those songs say Purchased, not Protected, about how many do you have that are Protected? If Music is the only media type being synced automatically, here's something you can try to figure out what specific songs are causing the error message... It could even be one rogue song.

Go to the iPod's Summary settings screen, and check the box for Sync only checked songs and videos. In your iTunes music library, show it sorted by Kind like before, select all the Protected songs at once, right-click the selection, and Uncheck Selection. After doing the Restore, set it up to automatically sync only Music. Choose to sync Entire music library (if your music library fits on iPod). Apply. iTunes syncs your iTunes music library to iPod, except for the unchecked songs (which are all the Protected songs).

Now, if you still get authorization error message, I don't know what's happening... If authorization message does not happen, checkmark a small number of the Protected songs, and sync again. By process of elimination (if the total number of Protected songs is not too large), see if you can find the specific Protected songs that cause authorization error message to come up.

Also, I don't think you mentioned your iPod model. In case it matters, what model iPod do you have?

All of your Protected songs are purchased songs from iTunes Store, from before early 2009. If any of your Protected songs are not songs you purchased with your current Apple ID, those are probably the ones causing the authentication error message. Protected songs you did purchase with your current Apple ID are not causing the authentication error message, because your computer is authorized for that Apple ID.

I didn't know you had iTunes Match. That makes things a lot easier. Most of your Protected songs will "match" songs that are currently sold on iTunes Store. On your song list, there is a column called iCloud Download. It is narrow, and the heading for column is a cloud symbol. If you don't see it, unhide it. Also unhide the iCloud Status column, if it's not visible. The iCloud Status column shows if a song is Matched or Uploaded (in iCloud).

Find a Protected song that is Matched. Right-click it and select Remove Download (not Delete). The local copy of song file is removed, but the song stays on your song list. The iCloud Download column should now show a cloud with download arrow symbol for the song. Click that symbol to download the song from your iCloud Music Library. Because it's a Matched song, you should get the DRM-free version. Its Kind now says Matched AAC audio file.

If you do this with your Protected songs, the only ones you have left will be those that cannot be upgraded because iTunes Store no longer offers them (they have Uploaded for iCloud Status). And any Protected songs that were not purchased with your current Apple ID will also remain, although I don't know how that's handled with iTunes Match. I have some Protected songs left in my iTunes library, but they are all authorized.